Sales: change and paid amount

I request to have a feature to enter the paid amount in both the second currency and the system currency rather than only in the system currency This helps me in Lebanon when a costumer pay in the second amount "usd" and the system is in Lebanese currency.

Example each 1 USD is 90000 L.L

So when the total is 135000 L.L. which is 1.5 UD and the costumer pay 1 USD the system will calculate the rest in 0.5 USD in the Lebanese currency (0.5* 90000= 45000). To add more, it helps when the rest is in decimal form.

Thanks.