Handling currencies in a database

How should money currency be handled in the database to be consistent? Should I choose the specific currency to use across my database or is it better to mix different values of different currencies? Let's say I have Product table, this product has a price, but what currency should the price be in? Should it always be the same or should I also have Currency column with currency code or CurrencyID pointing to specific currency? Should I set currency per product or globally per database? What is your experience with that?