Re: One of those places
A "no, thanks" without the theatre dramatics works fine, and actually shows you're a decent human being.
It's certainly not the cashier's fault. She hates asking just as much as you do. It's not like she has the choice to stop asking. Try not making her day just that much worse.
What got my goat was Barnes & Noble's habit of asking if you had a membership, then harping on how much you would save, then asking again, then asking "are you sure?"
It was so bad I stopped shopping there for several years, and apparently so did everyone else. Several local B&Ns went out of business, and now they don't even ask.