Turns out you can only use one discount code :/
I tried a few times to add the discount code information to headers, but no matter how I add it, I have not found a way I like to add them to the checkout screen for ease of use.
For now, find the discount codes on this page, and remember to use them at checkout.PS - these codes work for pick up orders too!
JANUARY
21-30; JAMMIN: 20 percent off your entire purchaseFEBRUARY
18-29; COMET: 20 percent off your entire purchaseMARCH
24-31; SPELUNKIN: 20 percent off your entire purchaseALL TIME
FREESHIP: free shipping on orders over 25 dollars??????: a code given when someone leaves a review; it's good for 15 dollars off a purchase