A complete dick leaves the tip in all pennies, in a water glass that has been flipped upside down. It’s a good way to demonstrate inertia and air pressure, but a bad way to leave a tip.
I just went through my change pouch and discovered $14.50 in silver and gold*, plus an unkown number of pennies, which I separated and placed in another bag.
Coins** are not an unwanted extra to us; a few loonies and toonies ($1 and $2 coins) can provide a complete if modest meal. So tipping with them isn’t a problem. I generally reserve some quarters and loonies for laundry change, and tip from what’s left over plus a fiver if necessary. The cost of my typical restaurant meal means that tips are seldom over $10, so there will certainly be coins there.
[sub]* “Gold” includes loonies and toonies. May not contain actual gold.
** Except for pennies.[/sub]
Back in the day I remember using subway tokens as part of what I was leaving as my tip. Eventually, everyone rides the subway in New York City…
What about a bagful of pennies for a hundred dollar meal? 
Most servers have to carry their own change, so I usually appreciated the coins (a lot of people would just leave the coins I left when I brought their change, which is fine too). Unless they gave the entire tip in change - that’s kind of crappy.
Though if the servers have coin-op laundry, those quarters may prove to be the best tips of the night!
Say what? You mean that if I buy a beer that costs $3.50, and I pay you with 3 dollar bills and 5 dimes, you can’t put that into the register? You have to put the 5 dimes in your pocket, take out two of your own quarters, and put them in the register? Do I have that right?
'Cause that’s all kinds of weird.
Bingo…I was a server for a few years and always loved getting quarters so that I could do laundry. I also worked in DC and Metrobus will take pennies, so I just kept a big jar at home of all the coins I received.
It’s high time that the end consumer no longer be obliged to swallow the cost or inconvenience of piles and pocketfuls of shrapnel coin. I say give it back to merchants, waiters, and anyone else you owe. The fact that the OP still leaves a reasonable tip in currency makes this more than reasonable.
Not enough people mind a monetary system skewed toward funneling this nearly worthless money into our pockets, but a lot of people whose job it is to receive money or sell things sure don’t want anything but nice convenient denominations.