What's the best way to add discount coupons to the Odoo POS?  I'm looking to add coupon mechanism where certain Items can be discounted from the invoice and not factored in the total price.  Instead, these selected items would get stored against the coupon 'code' as opposed to cash.  From the inventory/products side, I'd like to add a checkbox to the items that participate in this coupon program.  My question is: is this something that can be accomplished out of the box, or with an addon, or is this something that I'd need to program myself?

Thanks,

Henry