title: Magento add custom amount in checkout cart page
body: <p>I wanted to add a custom Fee to the cart total like we have discount ...
  But it should be added only when a condition satisfies , like if checkbox clicked from frontend by customer .</p>
  
  <p>Have referred : <a href="http://www.excellencemagentoblog.com/magento-add-fee-discount-order-total" rel="nofollow">http://www.excellencemagentoblog.com/magento-add-fee-discount-order-total</a></p>
  
  <p>But it adds by default .</p>
  
  <p>Please give any hint .</p>