Uh, no. I don't mind US dollars, but in talking about actual currencies used... no.
I'm okay with Credit, and there's two schools of thought here. The first one is that it doesn't matter what currency you use, as long as you have the money to pony up to pay for something. I don't want to be involved with currency rates when I have racing to do, cars to buy and maintain, or whatever else that involves credits... oh yeah, doing practice runs at race tracks. Credit is about as universal of a term as water. Think about it. When you play an arcade game, what do most arcade games tell you in the arcade's Attract Mode (the little demonstration of the arcade game from the title, to game footage, and even the "Winners Don't Do Drugs" screen)? Usually it will let you know how many coins or tokens equal one credit to play, and maybe even a notification for how many coins is one continue. To a game, you deposit in money to play, and that's a credit. Same goes for Gran Turismo games and most others using Credit as currency. When you have enough Credits in a GT game, you can get something. Your Credits credit you with almost anything you want in the game. I don't want to concern myself with currency rates or actual currencies. I can think of a game I played in which currency exchanging was featured, and that's the Super Nintendo classic "Secret of Evermore." I wouldn't consider different currencies. Let them all be the same to avoid confusion and even some frustration.
The second school of thought is that the credits for something varies. It could be designed to make more powerful and more rare cars more expensive, or also to probihit cheap skates from getting the best machinery for easy prices. I kind of thought that most of the bigtime Le Mans racers had rediculous asking prices for them. You pay 4.5 million Cr to get an Audi R8 or either Pescarolo. Can you believe it? In GTs 2 and 3, the highest asking price was 2M Cr. Now the highest is 4.5M. So, you have to work to get them, but those prices were ridiculous!