Hi Rachel,
You can setup Sales Line Discounts, from the item page, Sales / Line Discounts.
On that page Sales Line Discounts you can set these type of discounts per Customer, Customer Discount Group, All Customers and Campaign. What you need, is for All customers.
msdn.microsoft.com/.../hh898672(v=nav.71).aspx
Hope this helps. Best regards, Christiaan.