How are currency conversions performed on purchase orders?

I have a question regarding currency conversions on PO's. For example: If a subsidiary has EUR as base currency and the PO is filled in USD then the total amount is displayed in USD (which is good). But then when a saved search is created to display the amount, that amount is always displayed in a different currency. There is a field amount(foreign currency) but that includes tax. I would need the foreign currency amount without tax. The strangest thing is that the conversion is wrong as well (if you calculate it yourself with Netsuite's exchange rates, it doesn't add