Calculating SubTotal in a scripted search

I’ve seen other posts about calculating subtotal on an invoice (total – taxes – discounts – shipping) but this gets a little trickier with foreign currency.

I’ve tried starting with fxamount and then subtract out the other values after applying the transaction exchange rate.  However, the result ends up being distorted by rounding differences (when compared with inspecting the subTotal property if I just load the record).

Note: the script where I’m doing this is 1.0 so curious whether 2.x might solve this somehow.

Thanks!

Dan