To setup Discount for inventory based on quantity follow the below steps assuming the user has Accounting access

Goto Accounting module > Menu : Setup > Receivables/ Payables > Point of Sale Discount

The above setup is based on Discount Categories. To set it up Goto: Setup > Inventory > Discount Categories

Use this to setup a discount for the complete category with a 2 digit code

Assign a discount category to a product by adding the discount code.