Chrissy Calc is a fairly simple calculator app that was made with the retail worker in mind. It has a special function to apply a 10% discount and a function to add tax. The tax can be adjusted to your locale. This was originally made for my wife, a Kitchen Designer, and was also taught in my How to Make an iPhone course.
This calculator has all the normal functions you would expect from a general calculator including memory functions.
If you have any feedback please contact me at http://xbsjason.com.