I've NEVER seen that. I don't think you're paying attention. If you're paranoid, swipe it after the first item is scanned.
I swipe (almost always my debit card), change the payment type to Credit, or else Cancel when asked for a PIN, then wait for the total. At that point, the most I have to do is press a confirmation button, although some systems no longer require even that.
(For whatever reason, my credit union issues a transaction charge (25 or 50 cents, IIRC) for debit card purchases, so I always run it as a credit card. Online purchases automatically go through as credit cards. I've yet to get hit with the charge. Knock on wood.)