Oracle doesn’t allow multiple currency in a single Purchase Order, Does it?

in reality at our company procedure. there are some companies that have price agreement with us and there's a clause in the agreed contract to pay 80 % in $ and the other 20% in our local currency. as far as you know that, Oracle doesn’t allow multiple currency in a single Purchase Order. It always has to be a single currency. I believe this is same with Invoice as well.

* How we can solve such issue?

* Providing your point of view for this case.

* any solution?