# Why do we round off gasoline purchases, even when paying by debit or credit? **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [November 2, 2008, 3:39am UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673 "2008-11-02T03:39:42Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [November 2, 2008, 3:38pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/21 "2008-11-02T15:38:29Z")
Well, I see most of you are all complete nutbars, and I am the only normal one who always pumps an exact dollar’s worth of gasoline. 😉 ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [November 2, 2008, 3:40pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/22 "2008-11-02T15:40:47Z")
Let it go until the auto-shutoff does its thing. Overfilling the tank can damage your car, so I don’t do that. ---
**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\ **Post date:** [November 2, 2008, 3:45pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/23 "2008-11-02T15:45:46Z")
> [@Chefguy](#): > > Let it go until the auto-shutoff does its thing. **Overfilling the tank can damage your car** , so I don’t do that. Huh? I don’t believe this for one moment. ---
**Author:** ![What\_Exit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/what_exit/32/10652_2.png) [@What\_Exit](https://boards.straightdope.com/u/What_Exit)\ **Post date:** [November 2, 2008, 3:48pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/24 "2008-11-02T15:48:08Z")
> [@Chefguy](#): > > Let it go until the auto-shutoff does its thing. Overfilling the tank can damage your car, so I don’t do that. This really does call for a cite. I don’t believe you are correct in this belief. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [November 2, 2008, 3:53pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/25 "2008-11-02T15:53:37Z")
> [@Chefguy](#): > > Let it go until the auto-shutoff does its thing. Overfilling the tank can damage your car, so I don’t do that. Damage your car? Not really. What it CAN do, however, is cause gasoline spills and overwhelm your car’s vapor recovery system so that fuel vapors escape into the environment. And I don’t round off. No point to it. ---
**Author:** ![Spoons](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spoons/32/3141_2.png) [@Spoons](https://boards.straightdope.com/u/Spoons)\ **Post date:** [November 2, 2008, 4:47pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/26 "2008-11-02T16:47:25Z")
I don’t round off either. I use my debit card at the pump, and let it fill to however much is needed. It’s never an exact dollar figure (though oddly enough, it was once). ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [November 2, 2008, 4:49pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/27 "2008-11-02T16:49:38Z")
> [@Spoons](#): > > It’s never an exact dollar figure (though oddly enough, it was once). Why is that odd? It’s got to happen once every hundred times, on average. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 2, 2008, 5:49pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/28 "2008-11-02T17:49:16Z")
FWIW, I’ve been keeping track of gas mileage in the Prius since May. I never add more fuel after the pump has clicked off. Unfortunately different pumps shut off under different conditions. Nothing I can do about that. But by stopping fueling after the pump has clicked off, I’m trying to keep things the same from fill-up to fill-up. So the amount and price are what they are. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [November 2, 2008, 5:52pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/29 "2008-11-02T17:52:32Z")
> [@Johnny\_L.A](#): > > Unfortunately different pumps shut off under different conditions. And, in fact, the _same pump_ will shut off at different levels under various conditions. Nevertheless, I don’t think it’s going to make a difference of much more than about 5-10 percent either way. ---
**Author:** ![panache45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/panache45/32/64_2.png) [@panache45](https://boards.straightdope.com/u/panache45)\ **Post date:** [November 2, 2008, 5:57pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/30 "2008-11-02T17:57:16Z")
I don’t do it either. One of the few non-OCD things in my life. Damn, now you’ve got me thinking of doing it next time. ---
**Author:** ![mhendo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mhendo/32/3159_2.png) [@mhendo](https://boards.straightdope.com/u/mhendo)\ **Post date:** [November 2, 2008, 6:27pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/31 "2008-11-02T18:27:26Z")
> [@Fugazi](#): > > I always fill the tank all the way. That way I can calculate how many MPG I’m getting. Me too. My last 7 fill-up totals have been: $37.51 $38.30 $33.98 $36.11 $35.39 $33.17 $26.01 ---
**Author:** ![Mongo\_Ponton](https://avatars.discourse-cdn.com/v4/letter/m/eb9ed0/32.png) [@Mongo\_Ponton](https://boards.straightdope.com/u/Mongo_Ponton)\ **Post date:** [November 2, 2008, 6:38pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/32 "2008-11-02T18:38:10Z")
I always stop at even dollar amounts simply because I never considered that it could be any other way. Hell, I’d fill the ashtrays if I needed to squeeze just that extra 3 cents. I always wondered why they didn’t have some sort of electronic detent for making it easier. When the prices went up so much it became harder to stop at exactly the right spot and you might have to go to the next 25 cent increment and ruin the whole rest of the day! What the hell’s the matter with you people? There has to be order in the world. ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [November 2, 2008, 6:50pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/33 "2008-11-02T18:50:12Z")
> [@Q.E.D](#): > > Damage your car? Not really. What it CAN do, however, is cause gasoline spills and overwhelm your car’s vapor recovery system so that fuel vapors escape into the environment. > > And I don’t round off. No point to it. I’m going by what the owner’s manual for my old 2003 Honda CR-V said, which pretty specifically said that damage could occur. I’m not a mechanic, so have no idea why. After reading that, I quit topping off. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [November 2, 2008, 6:55pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/34 "2008-11-02T18:55:20Z")
**Chefguy** : The Prius manual says the same thing. I haven’t read it in a while, but it says that overfilling can damage the fuel bladder. Like your Honda, I don’t think it specifies what the damage is. ---
**Author:** ![Spoons](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spoons/32/3141_2.png) [@Spoons](https://boards.straightdope.com/u/Spoons)\ **Post date:** [November 2, 2008, 7:04pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/35 "2008-11-02T19:04:13Z")
> [@Q.E.D](#): > > Why is that odd? It’s got to happen once every hundred times, on average. True enough, so says the law of probability. But just as it’s possible to get a short run of good cards/dice/spins in a casino resulting in wins against what probability says happens over time (and vice versa), so it has been with me and gas fillups. In hundreds of pump-til-it-stops fillups, this has only happened to me once. ---
**Author:** ![j666](https://avatars.discourse-cdn.com/v4/letter/j/9de0a6/32.png) [@j666](https://boards.straightdope.com/u/j666)\ **Post date:** [November 2, 2008, 11:42pm UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/36 "2008-11-02T23:42:41Z")
> [@Leaffan](#): > > Huh? I don’t believe this for one moment. I’ve heard that for as long as I’ve been driving. No-one could ever tell me why. I don’t top off; some things it doesn’t hurt to take on faith. (It makes sense for Americans to remember 1492 and 1776.) ---
**Author:** ![Captain\_Carrot](https://avatars.discourse-cdn.com/v4/letter/c/f0a364/32.png) [@Captain\_Carrot](https://boards.straightdope.com/u/Captain_Carrot)\ **Post date:** [November 3, 2008, 12:10am UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/37 "2008-11-03T00:10:44Z")
> [@Fugazi](#): > > I always fill the tank all the way. That way I can calculate how many MPG I’m getting. Ditto. I also remember 410 (the first time Rome was sacked in 800 years), 1824 (US presidential election with four candidates, none of whom got a popular or EC majority, and the guy with the plurality in both was not elected), 1876 (another election, in which the Republican won by 1 vote even though he lost the popular vote by 3%), and prominent details of pretty much every Presidential election after 1932 or so. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 3, 2008, 12:13am UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/38 "2008-11-03T00:13:49Z")
I don’t always round off, but when I do, it’s usually because I have decided to buy fuel to a specific value - for budgetary reasons, perhaps, or if I’m presenting the receipt for reimbursement - something like that. ---
**Author:** ![Ruby](https://avatars.discourse-cdn.com/v4/letter/r/13edae/32.png) [@Ruby](https://boards.straightdope.com/u/Ruby)\ **Post date:** [November 3, 2008, 12:27am UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/39 "2008-11-03T00:27:44Z")
I think there are a lot more “round offers” than who are posting in this thread. I believe it’s a left-over from those days when people actually used cash to buy fuel. It was much easier to hand the attendant a $20.00 bill rather than $19.46. I was one who rounded off no matter what the currency until someone posed this exact question to me. My uber-intelligent response was something along the lines of, “I dunno, always done it that way, I guess.” Ever since then, I’ve just allowed the pump to stop and then I go on my merry way. ---
**Author:** ![gazpacho](https://avatars.discourse-cdn.com/v4/letter/g/6f9a4e/32.png) [@gazpacho](https://boards.straightdope.com/u/gazpacho)\ **Post date:** [November 3, 2008, 12:36am UTC](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673/40 "2008-11-03T00:36:40Z")
I always fill the tank because to do otherwise would mean spending more time at gas stations. [Previous page](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673.md?page=1) [Next page](https://boards.straightdope.com/t/why-do-we-round-off-gasoline-purchases-even-when-paying-by-debit-or-credit/470673.md?page=3)