We have made a customisation that allows you to % increase all currency rates. This is handy when operating multi-currency and you want to add a few % to the rates to eliminate risks of currency changes till you next update your list.
 
DickS

I suspect it would buffer you against any loss in exchange resulting from the way a payment handler calculates or charges?

Yes, it buffers the difference a currency might take before the currency list is updated again.
 
It ensures you always get the price you have set as base currency.