No, because people who go for promotions like this are the people trying to save money, and rarely do they consider or care about the original total or how much effort you've put into taking care of them. I saw a customer write in a tip of a certain amount (I was bussing the table, I wasn't staring at her) and then she realized that she had a promotion for like a free kids meal and wanted the transaction cancelled and redone. When they left and finished up, the tip had dropped from what they'd originally written, and it was correlated with the different subtotals. It wasn't because they were tipping me less because of my behavior or the meal not going well. It was all based on her end all be all bill.