Years ago there was a trend on credit card tabs at restaurants to list a handy guide to tipping. This saved customers the trouble of having to do math, which I have to guess had a positive effect on how much of a tip people left.
That trend never caught on, but recently at a restaurant here in Seattle (Agave) I saw it again.
The one thing that is missing here is offering the total. Why only do half the math?
Instead of saying “15% = $14.55″, it should say “15% = $14.55 = 120.77″.

Yes! I love/hate when they do this, without a total. I’ve never seen one with the total for some reason. Maybe even having a checkbox next to one? I hate the entire tipping process here, it’s absurd.
Wow, what an amazingly simple solution! You know that most of us would choose one of the pre-calculated numbers if only to avoid the math!
Actually, this reminded me of the power of defaults: http://sethgodin.typepad.com/seths_blog/2010/09/the-power-of-buttons-and-being-normal.html
Better still, pay the staff properly like they do in other civilised countries so we don’t have to tip at all. Everybody wins.