http://www.twopeaks.com/Tipper/
"While paying a restaurant bill, we make a mental decision about what percentage to tip based on quality of service. We then calculate the tip amount, and usually add a small fraction to round up the total to the nearest whole number."
I have found myself fumbling around with the built in calculator more than a couple times, to try and figure out the tax, tip, and ultimately my portion of the bill. Two Peaks latest application, Tipper, looks like a nice solution since it offers a handy feature I haven't seen on any of the other similar applications. Tipper will do a little rounding to make sure you don't have any fractions of a dollar to deal with. Best of all, it's totally free. So head on over to the Two Peaks website and download a copy.