I have a checkout field for tax exemption that is not related to a customer group. That would be too easy. Instead, I would like to update the tax amount and total to reflect those changes when this field is changed.
I have tried piecing together solutions to similar problems but nothing seems to do the trick.
So far what I have working is an observer on the
sales_quote_address_collect_totals_after event that gets the value of my field from the address and updates the tax amount totals. This successfully updates the tax, but does not update the grand total. As far as I can tell I cannot update the grand total in the same way.
I have attempted to call
$quote->collectTotals() and save the quote, but without success. It does not update the grand total to the correct amount.
Simply put, I need to update the tax amount, and have that change reflected in the cart total.
Any help would be greatly appreciated!