Retrieve Apple in-app purchase transaction tax amount

Question

I am implementing the API backend for Apple in-app purchases receipt validation. I wish to record the transaction including tax in a transactions table in my database for record keeping. How can I be able to retrieve the transaction details; amount paid and tax amount. Can my iOS developer pass me the tax amount in their REST call to my API for receipt validation. Or perhaps, with the transaction reference (unique_identifier or transaction_id) I'm able to make a REST call to apple after the fact. My Apple/iOS knowledge itself is very limited. Thank you.