You can set custom prices for customer groups. First create a customer group, then add customers. See the topic customer management for more information.
Custom prices per customer group can be set in the section Customer groups in product management.
A customer will see the custom price for his customer group after being logged in. Therefore, it's important that the checkout procedure is set to Account or Hybrid. Optionally you can add yourself as a customer and add yourself to a customer group. This way you can check if prices are displayed as desired.
Enter only numeric values for the prices.
Wikipedia: These are price reductions given for large purchases. The rationale behind them is to obtain economies of scale and pass some (or all) of these savings on to the customer.
When editing a product, you can set discount prices or volume discounts. This is also possible with product variations.
You can enter five quantity discount prices per product or product variation.
Leave the form fields empty and save to remove the quantity discount prices or customer group discounts.