Not at walmart, but one of our supermarkets in town has two self-checkouts. I tried them a few times, and they were so f-ed up that I gave up on them. One time, the machine did not accept any cash, but was stuck in the menu choice "pay by cash" without a "back" button. So I took my stuff to the normal checkout, which had the problem that my steaks had already been scanned. Solution: leave a bag of 20+ Euro meat at the checkout, and get a new one from the butchers shop.