Users will not have as much understanding of what a credit represents as opposed to actual local currency (Dollar in this instance). Even if 1 credit = 1 dollar that is still a mental calculation the user has to do, and there is also the extra consideration they have of "Is my 1 credit still worth 1 dollar...?"
A case in point - Microsoft back in 2013 decided to cease using XBox Live Points (credits) and instead converted everything into local currency. Their reason for doing so was:
This change was a direct result of customer feedback. You told us you want to be able to buy things using money instead of points, and we listened.
Making a purchase will be faster and easier than ever. You will see item prices expressed in local currency; no need to calculate what an item costs!
OK, it's only one case-study, and it could be argued that it's a different situation because 1 XBox Point did not equal 1 Dollar, but it does show that users prefer to buy things with actual money.
Initially, Microsoft had an actual business case for using credits (they're a global company and wanted to represent their items at the same 'price' everywhere in the world) but yet they decided to no longer go with that route based on user feedback. No doubt causing them a financial hit not only with the change to how it was displayed and handled electronically, but also changing all their marketing material, print outs, adverts etc to reflect the new pricing. I'm not sure (or at least you've not stated so) that you have an actual quantifiable business benefit for displaying them as credits, so I would stick to currency. People pay for things with currency, not with credits.