Using a digital currency instead of USD

Hi everyone,

For the concept of my site I would like to have auctions that don’t use USD or any sort of real currency. I am wondering if anyone has done or knows how to create my own ‘digital currency’ for auctions. Example: ‘credits’. Users would have a virtual wallet filled with his or her ‘credits’ that they can use to spend on auctions. Is this possible? Is there possibly a plugin that I could use.