The United States is 'Los Estados Unidos' in Spanish. Thus you can abbreviate to EU. But since Estados Unidos is plural it becomes EEUU to show this. So they only change money to American dollars or Euros, and not to the currency of other countries which use their own version of the dollar instead e.g. Australia.

EE.UU (Estados Unidos) = USA (United States of America) ;)

United States (of America)

There are dollars from diffetent countries in the world. So, if it says "dollars from EE.UU" means that only accept americans dollars.