It appears that the so-called "agency model" being used by several of the major publishers has another downside beside allowing them to sell their books at whatever retail price they choose without Amazon being able to discount them: you most likely are paying sales tax on them now, too. See this Amazon.com help page
for details, in particular this footnote:
Kindle books sold by various publishers 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.