I don’t know if it’s because I used the 30% off coupon for the TheraTears promo already, but I don’t see the 30% coupon for this Dentek deal, or the 30% coupon for the Dentek flossers either. So maybe it’s 1 checkout with the 30% off only — if so, maybe do all the 30% off deals in the same order.
Edit: from messing around, I’ve figured out that the 30% off coupon only applies to 1 item. Even if you have many items that qualify for the 30% off coupon, if you have them all in the cart, Amazon will only take off 30% from the lowest priced qualifying item, AND spread that savings across all the items in your cart that are part of the 30% promo.
Example: You have 3 items that are part of the 30% off S&S coupon. $30, $20, and $10. If all 3 items are in your cart, you will get 30% x $10 (cheapest) = $3 off. But the $3 will be spread across your 3 items proportionately; so the items would become $28.50, $19, and $9.50