I first read this as "nearest $100" and thought that you either eat at better places that I do or you're a very good tipper!!

My practice when paying by CC is to add about 18% (or more for great service) and then use the next highest dollar - so, to make it easy, if the bill was $100, that would be $18, and I'll just write $20 making the total $120.

When paying by cash I'll sort of do the same thing, hand the person $120 and say "keep the change" or "you're all set".

I think it would be rude to hand the person $120 and say "can I have $2 back, please"? Or, worst "50 cents" or even worse "64 cents."

If they grab the money and run to get change before I can stop them I'll tend to take away any small change and then use bills to make up the tip. I don't it "rude" but do find it "odd" to leave a bunch of loose change.

My mother, who was cheap beyond belief, would actually figure out exactly 15% and find the exact change. Even worse, she believed for some reason that you didn't tip on the tax. This whole thing just made it seem like a necessary chore as in "I don't like it, but I know I have to tip 15% but that's as far as I'm going" instead of "I had a really great time, thank you, here's a nice tip for you."