The best way I found is set up a specific price from the prices tab of the product I have added a screenshot below to show you how mine work
on this particular product if you buy 1 item you get it at the RRP if you buy 3 or more each product is reduced by 0.49p if you purchase 10 then they reduce by £1.59 each resulting in a single item costing £4.49 purchase 3 and they are £12 purchase 10 and they are £30
so to get what you want you would need to apply a discount of 5 including tax for the purchase of 2 products and a discount of 10 if you buy 3 products
Hope that helps
Paul
