Taxpayer means any person subject to sales and use taxes under the Nebraska Revenue Act of 1967 and subject to withholding under section 77-2753 and any entity that is or would otherwise be a member of the same unitary group, if incorporated, that is subject to such sales and use taxes and such withholding. Taxpayer does not include a political subdivision or an organization that is exempt from income taxes under section 501(a) of the Internal Revenue Code of 1986, as amended. For purposes of this section, political subdivision includes any public corporation created for the benefit of a political subdivision and any group of political subdivisions forming a joint public agency, organized by interlocal agreement, or utilizing any other method of joint action.