We have following scenario:

Our service shows the bill amount to the user in INR (Indian Rupees). For example Rs 1000
We want to receive full payment in INR in our bank account. That is, we should get full Rs 1000 in our account.
User selects his preferred currency as one of the following: USD, GBP, CAD etc based on the credit card he is carrying.
All the extra charges like Paypal fee + currency conversion charges should be deducted from the user's credit card.

How can this be done via REST API? We are using Python REST SDK.
The merchant is generally responsible for paying transaction fees and conversion fees. As far as I know there is no way to programmatically force the cardholder to pay them.
User's preferred currency is different from the product amount currency