The program connects to the internet at all times to keep up to date with currency fluctuations. However, if you don't happen to have internet access, it'll take into account the most recent estimates using its database.
You can also customize the application to keep track of your top 10 most usedcurrencies (in your case perhaps the normal thing would be to keep track of the Euro, Dollar, and Pound).
XE Currency is a useful tool for users who tend to buy things in foreign stores since a general rule of thumb is that things turn out to be cheaper if bought in that way. Needless to say, you should try out the program a couple of times.