Tatum first reviewed the tax schedule and invoices he sent the state. As he dug into the Northwest invoices, he remembered that some of them had various sales tax rates: some for 6.25 percent and others for 8 percent. He had even found a few with a 13 percent sales tax rate. He laughed as he recalled looking at those invoices; he knew that even with the city and special district rates, no Texas vendor could lawfully collect 13 percent.