How to pass already calculated tax total to Google Checkout HTML API

Question

I have a cart system that deals with selling alcohol and there are very specific tax rules for each item when selling in my state.

I want to use Google Checkout but I am unable to just pass the tax amount, instead, I can only find where Google wants to calculate tax rates for me, which won't work because you can't define the rules that I need in their GUI.

I just want to pass the tax total to Google ... i.e.

<input type="hidden" tax_total="12.17">

Any ideas on how to do this?

Answer 1

Other than sending your pre-calculated tax as a line item (order line item), you can look into Merchant Calculations API - it is however only available in XML API.

The premise in Google Checkout is that the only time a delivery destination is determined is after your buyer logs in and chooses or creates a delivery address for the order. That is why unless you have flat rates for shipping/taxes (for all possible delivery destinations), they will have to be calculated.