Depends on where you go. For one store I can think of in my area (Sam's Club, run by the same company as Walmart), they've been doing it for as long as I can remember (before self-checkout was even a thing). They've upgraded their receipt-checking process over the years.

Used to be that they'd just look at the receipt, look at what you got (the store didn't and still doesn't have paper or plastic bags for customers to use; customers can bring their own bags). They'd draw a line on the receipt and then draw a smiley face on it for the kids.

Nowadays, they scan a barcode on the receipt and then scan a few items randomly selected by their handheld that are in your cart. I think it's up to three items per receipt.