Tried this app while shopping the sales and it calculated close to the actual cost. I made a few errors as I didnt read where the 2nd disc is not calculated in when you add the items to the cart. One thing I did notice is that you cant enter less than .10 cents as in .01 to .09 and that threw off my calculations because Im anal when it comes to every penny.
RosBat about Sale Saver - Percent Off / Shopping Calculator