In order to enable product quantity discounts in your store, the Discount Option needs to be enabled. Navigate to Discount Setup screen from the Store Admin Menu and select the option titled “Enable Product Quantity Discounts” as depicted in the following screen shot:
For more information on the Discount Setup screen, please see the Discount Setup section.
Next, the Product Quantity Discounts Setup screen needs to be configured. Please see the Discounts By Quantity Setup section for more information.