Setting, adding and changing tax by default becomes by default from Settings, category Tax by default. Setting is carried out by the field where you have 3 options - 0%, 10% and 20% retained by the Save button.
                  If you want to change, click Edit, transfer to a new page with two fields to fill in where you can write two different values, and in the Tax field you can also enter text.
                  Adding it to the right of the button Add, again jump to a new page with two fields to fill, enter the values ​​you want and save the changes.