(a) A person is entitled to a credit against the tax imposed by this article on the use of a particular item of tangible personal property, custom software or service equal to the amount, if any, of sales tax lawfully paid to another state for the acquisition of that property or service: Provided, That the amount of credit allowed does not exceed the amount of use tax imposed on the use of the property in this state.
(b) For purposes of this section:
(1) "Sales tax" includes a sales tax or compensating use tax imposed on the use of tangible personal property or a service by the state in which the sale occurred; and
(2) "State" includes the District of Columbia but does not include any of the several territories organized by Congress.