How can I make a currency conversion in b2c application

We have a b2c application for which we are introducing multiple currencies.

This should happen when we get the product feed(or a daily job) and should create a price row with the new currency for all the products according to the conversion rate we provide in the currency model. Now how can we handle this and where can I convert the already existing USD to say JPY.

New to this particular concept, doing my research, any advise would be helpful.

Thanks in advance.