Hello,

I would suggest the following:

Invoice cannot be posted unless update Taxes is clicked.

To do so, simply add a boolean field, by default it's False.

Then in your Update taxes, update its value to True.

Then in Posted Action, say:
If my bool is False: then display message like "Please Update taxes before posting the invoice"..

def action_posted_or_whatever_the_name_is(..):
if not my_boolean:
raise UserError(...)
return super(AccoutnMove, self).action_posted_or_whatever_the_name_is(..)

def Your_update_taxe_func(..):
// your code
your_invoice_variable.my_boolean = True

This is if you want to have A visible message to display.

But if you want to update taxes directly, you can call "Your_update_taxe_func" in the 'action_posted_or_whatever_the_name_is':

def action_posted_or_whatever_the_name_is(..):
self.Your_update_taxe_func()
return super(...).action_posted_or_whatever_the_name_is(..)

Hope this helps.