If you want to enable currency switcher in your header than follow this easy step.

Step 1: Admin setting
You might have noticed the ”Currency Setup” tab in Magento’s Administration under “System->Configuration” menu. There you should select default site currency, and besides that, all currencies you want to support.

After that, you should go to “System->Manage Currency Rates” and set rates for currencies you’ve chosen before. You can use Webservicex to import currency rates from Webservicex service. Here’s how it looks like:

Step 2: Open /app/design/frontend/default/[YOUR THEME]/layout/page.xml
Add this line of code

<block type="directory/currency" name="currency" template="directory/currency.phtml"/>

After

<block type="page/html_header" name="header" as="header">

Step 3: Open /app/design/frontend/default/[YOUR THEME]/template/page/html/header.phtml
Add

<?php echo $this->getChildHtml('currency') ?>

After

<?php echo $this->getChildHtml('store_language') ?>