Some states shipping is taxable, and others not. We've found a great resource to assist you in finding out if it is legal for you to charge tax on the shipping amount charged to your customer.
As with any tax-related matter, we recommend that you also seek advice from your tax professional and your taxing authority.
Tax Jar: Is Shipping Taxable?
Avalara: Shipping and Sales Tax Explained
See article, Helpful Sales Tax Information for additional external information.