Take a look at http://drupal.org/project/uc_currency_convertUbercart Currency Conversion. From the project page:

This module converts prices of ubercart products from one currency to another currency. The target currency will be selected as follows

1. Administrators can select the currency and force all prices to be automatically converted
2. If the above is not set, then the currency is determined based on user's address
3. If the above is not possible, then the site's default currency is used.

The module depends on Currency module.