Again I’ll state the real reason is people assume storekeepers will round UP not down.
As for taxes it’s simple. You would price your items to come out to end in 0.00 or 0.05 AFTER taxes.
When I worked at Red Roof Inn about 15 years ago I HATED making change. So I charged weird rates like 26.93 so with tax it came to like 30.00 even. (I worked graveyard so they let me get away with murder)
I remember reading about this a few years ago and IIRC there were a few stores that did round up the total to the nearest nickel (I think the article had to do with something about the usefullness of pennies). They had this sign that said they were going to round up the total and donate the “rounded up amount” to a local charity.