Sales tax on shipping depends on state or provincial tax laws and may be fully taxable, partially taxable, or not taxable. Review local tax requirements to determine whether shipping charges should be taxed, and configure your tax settings accordingly.
As with any tax-related matter, we recommend that you also seek advice from your tax professional and your taxing authority.
From the sidebar navigation, select 
Settings, then Preferences.
For the US, select the Invoices tab, then enable Add Sales Tax for Shipping. When finished, select Save.
For Canada, select the Tax tab, then enable each Shipping option for your applicable sales tax type. When finished, select Save.