Forgot, there's another solution you could also use. You could use CBSubs Promotions then apply a negative promotion to every purchase. Then on the "Display" tab of your promotion you can supply a custom price display. Promotions can even be location based (not as much as Tax) by using the access parameters on the "Groups" tab of your promotion. The downside is the conversion rate won't be automatically calculated and you'll need to manually update it as needed.