Hi, The exchange rate on the order is automatically obtained according to the currencies settings. Of course, you can customize it to modify it, although it is not recommended.

And general financial personnel will perform the following operation at the end of the month, so different exchange rates will not cause problems.

In addition, I have encountered customers in your situation and suggest to calculate manually outside the system and then fill in the local currency amount in the system.
Hope this can give you some hints as well.
Thanks.
ZHU