The European Central Bank has a site for daily currency rates in XML.
http://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml
Some more info here: http://www.ecb.int/stats/exchange/eurofxref/html/index.en.html#dev
You should probably load and parse the XML on startup and also save it for offline usage and so that you don't have to fetch the values every time(once a day is enough).