I emailed Amazon about this very issue a couple weeks ago when I saw sales tax on my ebook purchase for the very first time. I received the following answer:
Date: Jul 13, 2010 5:07 PM
Recently, several publishers modified their relationship with Amazon to a business model whereby the publisher, not Amazon, sells the Kindle book. Kindle books sold by the publisher are subject to sales tax based on the publisher’s state tax reporting obligations and the taxability of digital books in those states.
As a result, sales tax for Kindle books sold by the publisher may differ from the sales tax to which you’ve been accustomed for Kindle books. Kindle books sold by Amazon Digital Services, Inc. are subject to sales tax in Kentucky and Washington State.
You can find additional information about sellers and states that collect sales tax in our Help pages here:
I hope this helps. Thanks for your interest in the Kindle Store.