Enter payment for purchase order in local currency

We have some overseas suppliers who we pay in their currency. When trying to add the payment to our Purchase Order Invoice we often can't get the payment to balance with what we actually paid in our local currency (it's out by a few cents) which is an issue when it comes to syncing with Xero. 

I would think it would be logical to enter the foreign amount paid, and the actual payment amount in our local currency and the exchange rate is calculated automatically.

Currently you can only enter the amount paid in foreign currency, then you need to manually figure out the exchange rate by what you ended up paying in your local currency, then sometimes the rounding makes it impossible to get DEAR to show your actual amount paid.

I have tried adding a rounding line to additional costs with +/-1 cent, but sometimes it still wont balance.