<img src="http://i.imgur.com/7nADyjL.png" />
I created a custom module which applies a discount on a sale order line if the quantity is >= 6 .
For this I did override a _fnct_get_discounted_price functional field of sale.order.line (which is defined in website_sale module).
In the above problem a discount of 0.5% percentage is applied on sale.order.line if quantity is >= 6 as intended.
But the Total is still calculated using the original price instead if discounted price.
ie Total should be 6 x 75.05 + 6 x 1709.05= 10704.599 instead of 6 x 79.00 + 6 x 1799 = 11268