Shopify Scripts for Tiered Pricing
Tier Pricing is a way to encourage shoppers to buy larger quantities of a product by applying discounts based on the quantity ordered. These discounts may be “tiered” so that they increase as the order amount is raised.
UPDATE on this ( 23 Feb 2018)
if you want to give a discount to cart price based on tags of certain products
Cart – 15 quantity – total value – $300
Item tagged – 10 quantity – $200
item not tagged – 5 quantity – $100
Discount should be based on quantity, Now we should give discount as 10% of cart it should be around $30