jsStore

I have been using jsStore on one of my sites and m quite please with how it works. I am not trying to integrate it with an affiliate program and to do that I need be be able to take the total value of an order, save that value to another variable (tcost) and make that variable available to my finish page.

Sounds simple, doesn't it? Problem is, I don't have enough knowledge of javascript to figure this out . Anyone out there who uses jsStore or knows enough about it that they could help me with this?