No, Mudguard's solution is the correct one. If you sell something for $100, sales tax included, the actual selling price is 93.90 (100/106.5). The tax at 6.5% would be $6.10. I've done sales tax reports in Michigan and I know here that, no matter how much you collect by using the state's tax tables, you send in 6% of your sales at the end of the month.