To the right of the "Related" tab, you will find the "Discount" tab.
This section will allow you to offer bulk pricing discounts on items.
For example, users purchasing 1 or 2 of the item will get no discount at all. However, if they purchase between 3 and 5 of the item, you can offer them a percentage discount on each unit purchased. You can add as many ranges as you desire for the bulk discounting.
Furthermore, the Product's listing page will contain a small chart indicating to shoppers of the bulk discount pricing that is available.