If you use your credit card out of the US or USVI (and probably the territories) there will be a foreign transaction fee (unless you have a card that has no FTF). Even if the charge is made in US Dollars there will be a foreign transaction fee because the card was used outside of the US. Charging in US Dollars in foreign countries is called dynamic currency conversion and will always result in a worse exchange rate the being charge in local currency. The DCC will always be in the interest of the merchant and not the purchaser.

When we were in GC they said it was an island law that all charges were made in US Dollars. we had every merchant tell us this. There is a local currency but every merchant refused to use the CI currency for credit card transactions.