Opencart add discounted prices in checkout page

Hi,
I have made an eCommerce with Opencart. The reference site is http://gmentr.com/msplocart/. When you will go to the site and when you will click on buy now it will show you different product quantity with discount price option. Now I want that when I will click any of the discount option it will directly go to the checkout page and the desired quantity and price that has been used in discounted price option. Is it possible to do this in opencart? If yes then how?

Any help please I am really stuck with this point