Creating and Switching between Currencies

Change your GBP, EUR and DOL queries to a merge with the exchange rate file.
The amounts as a new base currency column eg all GBP. 

Then create a Currency pick list table

and this measure

GBPAmount =
SUM(Sales[GMPValue)])

Sales in currency =
VAY myexchangerate= SELECT(picklist(Exchangerate))
RETURN
[GBPAmount] * myexchangerate

The either add a slicer with the picklist(Currency)

or use the filter menu to specify the picklist(Currency) for each visual.

Drag the [Sales in currency] to your visual and it should work.

Please click thumbs up and Accepot As Solution, thank you !