Scenario
A Norwegian legal entity is established with Accounting currency = USD.
Sales codes are set up with Sales tax currency = NOK as required by the tax goverment.

The legal requirement for sales tax deduction is to post the sales tax with the currency exchange rate from the vendor invoice document. Using the standard exchange rate will result in differences and conflict with the legal requirements.
IDEA:
The user should be able to specify the exact exchange rate stated on the invoice to get the correct sales tax deduction in NOK. The currency pair for the Sales tax exchange rate should be Transactions Currency - Sales tax currency.
Ex :
A vendor invoice in EUR should be calculated based on a specific EUR/NOK exchange rate.
A vendor invoice in USD should be calculated based on a specific USD/NOK exchange rate.