Hiya
Its something to do with your settings in your paypal profile (I had a problem where the postage was not being picked up)
This is what I did to resolve it.. I know mine is postage, but you can change the payment types as well
From Paypal, you need to select Profile (from the top links) then Postage Calculations.
Can you check that the tick box "Click here to allow transaction-based postage values to override the profile postage settings listed above (if profile settings are enabled)."
at the bottom of the page is checked. If it isn't, every transaction will use the postage prices defined in the ranges on that page.