Back in the 1920s/30s when sales tax was introduced, companies had to decide whether to include the tax in the item's price, eat the cost, or pass it along to the customers. As we are all painfully aware, it was passed along to the consumers. This is a really creative way of combining credit/store card rewards with sales tax in consumer's minds. Of course money is fungible, so it doesn't matter if the reward is covering sales tax or just a fixed percent (although the later could be higher than most fixed percents depending on state). Regardless, an interesting experiment.