Currency module step by step guide
You can also use below modules :


Yahoo! Finance currency converter



  This module provides Currency with currency exchange rates through
  Yahoo! Finance, which are updated continually throughout the trading
  day.



Currency Converter



  Currency converter module was created for quick currency convertation.
  It contains 10 currensies.
  
  It is flexibly configurable block. The currency undertakes from
  several banks (on a choice).



Open Exchange Rate Money.js



  This module provides support for the money.js currency conversion
  script from http://josscrowcroft.github.io/money.js/ along with
  support for the Open Exchange Rate currency conversion data.



Exchange Rate



  Exchange Rate API is an extensible module that allow users to display
  and manage the exchange rate in countries from around the world.
  
  Is common to see tools that present the official exchange rate, the
  problem is that each bank has his own rate, for this reason it is
  important to have a tool that can show the different variations across
  multiple financial institutions.