klackMassdrop is based in CA and has shipping facilities in at least NJ, so if shipping to either of those states, you have to pay sales tax. If you can ship elsewhere you don't! I am not sure where Z-Packs is based, but unless you are in that state, you don't have to pay tax directly from them.
JoomyZpacks charges 4.95 for US shipping on orders less than $100. Anything over $100 is shipped free of charge. They are located in West Melbourne, FL. If outside of Florida, no sales tax is charged.
tedder.reedFair enough. So if you live in CA or NJ this may not be a good deal. But for most people it is a (small) discount. Actually it seems like the biggest savings are for people outside the US since Zpacks charges $45 shipping to Australia for example. Being Australian I'm not complaining ;)