Honestly, I'm not devious enough to work this one out. But there's a scam somewhere in the observation I'm about to make. (A highly illegal scam, I'm sure; please don't try it on your own.)
I have been using dollar coins to buy stuff. Almost every cashier looks at these coins and asks, "What is this?"
"Dollar coins," I reply.
"Oh," they say, and they duly ring them up.