Paypal shows different costs

[wish2]

Hi, We are using Virtuemart with payments going to paypal. Virtuemart adds everything up fine but as the customer passes to PayPal the costs change and also Paypal adds a postage value which has already been costed in virtumart/joomla. Please can you help?

[stinga]

Have you set PP to add postage?
How do the costs change.
Some examples please, my crystal ball is in for its 100 service.