We had no problem anywhere using U.S. currency. Some vendors will say they only have change in peso's but with a little proding and the possibility of you walking away from the deal they seem to produce change for you. The only advice I would have for you is to have lots of small bills with you. After PV I made sure that almost all of my money I took to shore was in 1's, 5's, and 10's. If I was going to buy stuff from a store then I used my credit card.