Before leaving the cashier's stall, check your receipts for "cash back". The clerk can do this yet you don't get your money because you didn't request it and she didn't tell you. She gets your money. Demand that either she deletes all your purchases and rings them in correctly or demand to speak to a supervisor who will have the clerk make the necessary changes. Again, check the receipt. You'll hear all kinds of excuses, but stand your ground and make them do it right.