1 penny for piss poor service, only because i actually had a server chase me out of a restaurant once claiming that i forgot to leave a tip, i said i know there is nothing there, but i didnt forget anything, the penny makes it crystal clear that it was a piss poor performance and the tip wasnt just forgotten.
average service gets somewhere between 15 and 20 depending on if i have cash to pay the tip, or rounded up to the nearest dollar on the credit card.
great service or just doing something that i see as above and beyond has been known to result in 33 to 50%. Repeat places where they remember my kids names get bonus.
One thing i recently found out is that sonic, americas drive in, pay based on tips, so they get the 3 dollar or whatever wage. which is really kind of sad, its fast food as far as im concerned.