Not knowing what record-keeping method you have, you can make copies of the Amazon invoice to match the number of categories that you need to classify your purchases for. Then maybe highlight the items on each invoice that go in each separate category, and mark each invoice with the corresponding category. Total the $ amount that you're allocating into each category, including your sales tax paid.
That's just a suggestion.
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*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***