Currently Jamroom DOES NOT offer any pay-per-download features, at least not in the same manner as iTunes. This is something that is currently being worked on though, and my hopes are to able to offer it to Jamroom sites sometime soon. For those looking to offer pay-per-download services in the mean time, I recommend the following:
Using Weed Files in Jamroom
I HIGHLY recommend checking out the Weed File Sharing System. This system gives you all of the benefits of a file-sharing type system (i.e. your visitors can download the files for free), but guarantees that YOU and the ARTISTS get paid for the work. With only very slight modifications Jamroom works very well with Weed Files. Check out this post in the FAQ for details on using Weed with Jamroom.
Zen Cart shopping cart software
Also, some Jamroom owners have been successful in getting the Zen Cart shopping cart software integrated with Jamroom, which has allowed the sale of media downloads. Note that Zen Cart is NOT developed or supported by Jamroom, and I recommend you fully investigate the worthiness of any product you wish to incorporate in to your site.
Jamroom's Integrated PayPal Store
Another option is to simply use Jamroom’s built-in PayPal store. While this method involves more manual steps, it is guaranteed to work. Simply offer a Lofi version of the song on the Artist Page, and then “sell” the CD or down-loadable songs from the Artist Store. When the artist receives notification from PayPal that someone has purchased their album (or song), they simple e-mail or offer for download the tracks, or ship the CD to the customer.