I sold 11 separate things. I noticed that the total price approximately 130.00 had only produced a 16-dollar discount. If I put the 11 items in numerical order by high to low price the two highest should have made the third one free, but it did not work that way. The numerical order or time of order, which is the proper way. I calculated that there was another 18 dollars that the buyer should have gotten but did not get. I'm losing sales. Is that a programming error?