Dash into that shop, grab the stuff you need, go to the cashier who scans the items, wave your card on the reader, "No receipt needed thanks" and off you go...
This morning I popped into a well-known craft store and picked up four rolls of brown wrapping paper. They were £3.30 each or £3.00 each for a multi-buy. I knew this because I had looked up online to see if it was stocked before going to the shop. One thing I can do is my times tables! Four times three is twelve. "£34.80 please," the cashier requested. I withdrew my hand from the reader. "Can you check that please?" I asked. She did. "Oh," she said, "I thought that sounded rather a lot. The machine scanned the wool again that the lady in front of you had just bought when she was putting it into her bag. Sorry." "No problem," I replied.
But that's why I always ask for a receipt.
Happy shopping - until Thursday.