As the rewards are all subtracted from your plan price before taxes, that means that you do not have to pay on the discount. The tax will be calculated on the net amount owing after all discounts have been applied.
It would be before taxes. It would be part of the subtotal, no different to when you buy a product in retail and you have a coupon/credit that lowers the price. Taxes will always be the last line item before the grand total.
