So here is my theory: Download the TipKalc for your iPod and even though it costs $4.99 you'll end up saving money.
If you don't have a fancy schmancy cell phone with a tip calculator the TipKalc widget for your iPod might be the answer to all your dinner-table scribbling woes. You just spin your iPod click wheel until you get to your bill amount and everything is calculated for you. Tip amounts and grand totals appear on either side and you get the choice of 20 or 15 percent so you can decide how great your service was and tip accordingly. It also gives notes for splitting the check 5 ways.
It's compatible with iPod nano, iPod with color display and video iPod. Download here.