I've ordered from Amz through my aunt in Wash state and as far as I understand it, some items are taxed and some aren't, depending on where the items originate.
Directly from Amazon.com gets taxed. Third party sellers, no tax. Despite having to pay sales tax, I still do most of my online shopping from Amazon.com. The Amazon.com Prime shipping definitely pays for itself over the course of a year. The best way to buy things is from third party sellers who have their orders fulfilled by Amazon.com. No tax, Amazon.com Prime shipping. Nice.