Extend Opencart to allow for both Special prices and Quantity Discount (Multibuy) Prices.
By default Opencart only allows for the use of one of these options and if they are used together by default the Special Price will be used. This is not always useful, say you want an extra discount for quantity on the special price?
With this extension you can use both. It will automatically select the cheapest option, saving you any angry customers should they be charged more than "advertised" and includes a feature to let the customer know which price has been selected to give confidence in your store and make it easier all round.