Possible to add tax values based on API response?

Hey, Mike. Thanks for taking an interest. It’s actually just a custom-baked REST API created by the client that integrates with their CRM and local databases. I send a query that looks like this:

{
    "customerno":"ABC0001001",
    "state":"Georgia",
    "zip":"56544",
    "zipplus":"0000",
    "volume":"1,100.0",  // cart subtotal
    "freight":"10.5"  // shipping costs, also calculated via API
}

And it returns JSON like this:

{
    "state": 76.346875000000011,
    "county": 5.5525,
    "city": 0,
    "district": 0
}

Those tax values are based on the client’s internal tax tables, customer non-profit status and some discount programs.

Again, I’ve considered just disabling WooComm tax entirely, and tacking these values on to the cart as “Fees.” But if there is a good tax action hook or programatic way to directly inject tax values, that would be preferable, I suppose. As a last ditch, I think I could get them to edit the API to return the rates rather than the values, but even then I’m not 100% sure what the ideal approach would be… Any thoughts? Resources to help me look into the issue of tax calculation further? I know there’s a way to make this work.

Took a look at Taxamo. Could be wrong, but it seemed to me like they are still relying on rates, even if they are getting those rates via an API call. Thanks for the tip, nevertheless.

Just to test the idea, I disabled all taxes and tax calculations from the Admin panel. I then plugged my API query logic into a new function in functions.php:

add_action( 'woocommerce_cart_calculate_fees','woocommerce_custom_taxes_as_fee' );
function woocommerce_custom_taxes_as_fee() {

		// JSON for API call formulated and sent
		// API response JSON received and tabulated as $total_tax

		$woocommerce->cart->add_fee( 'Tax', $total_tax, true, '' );

		// Error checking code, too, of course
	}
}

Basically, because I named the fee “Tax” when I call add_fee(), it displays in the cart just below the subtotal exactly as if it were the standard tax calculation. The values I want get plugged in, the customer is charged the correct amount, and the amounts are tracked as necessary…

Not exactly semantically on point but it seems like a good solution. Can you think of any potential downsides? As long as it’s well-documented and maintained, I hope this is a decent solution for this use case.