Kazantip! app for iPhone and iPad

Its fairly simple to do the math on a 20% tip, but what if you want to leave a tip such that you leave a minimum percent, but also tip an amount such that your total will be a checksum, or a palindrome, or both?

When you enable a checksum, the pennies digit of your final total will be a sum of all of the other digits of the number, so in the total of $147.02, the 2 comes from 1 + 4 + 7 = 12. Its then divided by 10 and the remainder taken, because only one digit fits in the pennies.

With palindrome turned on, your total will always be a palindrome, such that your credit statement will report that you paid $147.41.

This prevents dishonest vendors from adding additional tips onto your receipt. You can easily look at your statement and identify with some certainty amounts you actually tipped.