I really enjoyed the well-documented Google Checkout XML API, although I could not find any API method to determine the Google fee for a transaction. In fact, I could find no mention of Google fees in the API documentation!
To Google's credit, Google Checkout was a free service in 2007 while they were in beta and rolled out the fee structure on January 1, 2008. And Google offers free payment processing until 2009 for approved non-profits.
But come on Google, PayPal provides API access to the processing fees! I think ecommerce merchants would like to be able to reconcile processing fees without the additional step of logging into the Google merchant console.