MarketPress Plugin is Doubling the Amount Due at Checkout

Hello:

I'm writing because I'm having issues with the price of the order doubling at the payment processor site (2Checkout payment gateway). For example, a customer adds an item that costs $10 to their cart. Upon checking out and being transferred to the gateway, the total amount due would be $20.

I contacted my payment processor and received this message:

The way that 2Checkout works is that your website passes us sale information, and we charge based on that. If we are charging $2 for an order, we were passed $2 for the purchase price of that sale. I attempted to test this on your website, but was unable to do so because your site would not load in my browser, so we could not place a test sale.

This has happened multiple times with different users and it is unsustainable. Do you have any insight as to why this is happening?

Thank you,

Stephen