If your store is not adding the taxes on your grand total, as follows, and you are within a PHP7 version:

You can do the following things:

• Try changing the following config parameter:
  
  1	admin > system > configuration > Sales > Tax > Orders Invoices > Include Tax In Grand Total

• Install this module with the following quote overriding:
  • https://github.com/amper88/magento-php7-taxtotals