The sales and use tax is computed on:
(1) the taxable price of each separate sale;
(2) if a combined sale is made, the combined taxable price of all retail sales on the same occasion by the same vendor to the same buyer; or
(3) if retail sales of tangible personal property or a taxable service are made through vending or other self–service machines, 94.5% of the gross receipts from the retail sales.