One of my clients shared with me a way to get the info out of Amazon.  Lemme see if I can find it . . .

From a browser (not an app) log in to your amazon.com account.  Pull up "Your Account".  Scroll down a bit, on the left side under "Ordering and shopping preferences" you should find "Download order reports"  Click it.

On the right side under "Quick Set Options" click on "Last Year (2017)".  All that does is automatically put in the Start and End Dates for you, but it beats entering them yourself.

I'd recommend the "Items" report since one order may have multiple items, some of which have sales tax and some don't.  You can give it a name if you want, like "2017 Items".  Click "Request Report" and it will generate a csv file that you can open in Excel (or Google Sheets or OpenOffice).  Column AC is the tax collected.  Sort/filter/whatever you'd like to remove the ones that do have sales tax.  Total the AB column for the rest.

We have an extra annoying step in VA because the sales tax rates are different on groceries vs. non-groceries.  So the AmazonFresh stuff (or Hello Fresh, Blue Apron, etc.) has a lower tax than other things.  There may be some massaging of data needed.  But it's better than not having any data at all.

It's always existed (and I've been paying it for as long as I can remember) but in 2016 VA began requiring a response so I have a blurb that I copy/paste and email to clients.  Most of them say no, but some give me numbers.

Rick