1) Click 'Payment Options' under the 'Commerce' heading of the Control Panel.

2) Under the 'Tax and Insurance Settings' heading, edit your tax and insurance settings.

3) When you are finished, scroll down & click the 'Save' button.

Updated
1) Click 'Payment Options' under the 'Commerce' heading of the Control Panel.
2) Under the 'Tax and Insurance Settings' heading, edit your tax and insurance settings.
3) When you are finished, scroll down & click the 'Save' button.