No, the Quantity Breaks app applies the discounted pricing in the cart before the customer proceeds through the checkout process.
Whatever price is in the cart is the same price used for shipping.
The Quantity Breaks (standalone) app is no longer available for new installations. If you are currently using Quantity Breaks (standalone), you will be able to continue using the app on a grandfathered plan.
Any new installs of the Quantity Break app will be redirected to Custom Pricing which has a Quantity Breaks plan available. For more information on Custom Pricing, please visit Custom Pricing: Information and Overview.