It seems likely, assuming you're using a card with those fees.
If you use a card w/o those fees, probably not.

Are you looking at a major purchase? Small purchases are probably best made with Pesos (though probably not in GC ) The vendors will rip you off 10-20% in the currency exchange.

GC runs on the dollar, but I'd have to assume (to be safe) that even charges made in green backs will incur the fee. After all, the fee is about making money...

If you do intend to make charges, don't forget to register the card and bring a backup card if possible.