Different Rate of Item for Tax Calculation

When creating purchase order of an item imported from abroad, my client come across a problem which we need to resolve,

  1. He/She creates the purchase order with item rate in the market on that particular day. Let say $100 / Kg
  2. But when the consignment reaches the port, customs charge a duty on the rate of the commodity for the day it reaches the port. Let Say $110 /Kg
  3. Then there are few Taxes and duties needed to be added for shipment and dependent on custom duty.

The problem is if the client changes the basic rate of item from $100 to $110 then the supplier would be paid more than decided.

If there is a workaround to this problem? or I need to do customization anyway. If so then any pointers please!

Please check landed cost voucher functionality link

Yes I am aware of it BUT it takes away the whole functionality of accumulating and calculating taxes automatically on the basis of rates applied.