Zend_Currency offers you the following benefit:
Complete Locale support
This component works with all available locales and therefore knows about more than 100 different localized currencies. This includes informations like currency names, abbreviations, money signs and much more.
Reusable Currency Definitions
Zend_Currencyhas the advantage that already defined currency representations can be reused. You could also have 2 different representations for the same currency.
Zend_Currencyallows you also to calculate with currency values. Therefore, it provides you an interface to exchange services.
Zend_Currencyincludes several additional methods that offer detailed informations about currencies like which currency is used within a defined region and what are the known abbreviations of a currency.