National Retail Sales Tax Act of 1999 - Repeals the income, estate, gift, and certain excise tax provisions of the Internal Revenue Code.

(Sec. 4) Amends the Internal Revenue Code to impose a 15 percent tax on the use, consumption or enjoyment in the U.S. of any property or service produced or rendered within or without of the United States. Prohibits, subject to exception, imposing a tax on any property or service purchased for: (1) a business purpose in an active trade or business; or (2) export from the Unites States for use or consumption outside of the Unites States, provided that the purchaser provided the seller with either an intermediate sales certificate or an export sales certificate. Defines "purchased for a business purpose in an active trade or business" as property or services: (1) purchased for resale; (2) purchased to produce property or services; or (3) purchased in furtherance of other bona fide business purposes. Sets forth rules relating to the obligation of governmental units and not-for-profit organizations to collect, remit, and pay taxes. Sets forth provisions concerning credits and refunds.

Allows for general credits against the tax, including: (1) a used property credit; (2) a business use conversion credit; (3) an administration credit; (4) a compliance equipment cost credit; (5) a bad debt credit; (6) an insurance proceeds credit; and (7) a transition inventory credit.

Provides for installment payments of the tax on the purchase of a principal residence.

Allows an eligible family unit to receive a sales tax rebate. Requires that a family member, to be counted for the purposes of determining family unit size, must: (1) if over two years old, have a bona fide Social Security number; and (2) be a lawful U.S. resident. Declares that no individual shall be considered part of more than one family unit.

Sets forth definitions and special rules concerning such things as: (1) foreign financial intermediation services; (2) financing leases; and (3) installment sales. Imposes a 15 percent tax on gaming services.

Directs an administering State to administer, collect, and remit to the U.S. Treasury the tax on gross payments for the use, consumption or enjoyment of taxable property or services within the State. Defines an administering State as one which maintains a specified conforming sales tax and enters into a specified cooperative agreement with the Secretary. Provides for administrative support for States.

Sets forth provisions concerning, among other things: (1) monthly reports and payments; (2) records; (3) penalties; (4) appeals; (5) accounting; and (6) hobby activities.

Authorizes the Secretary of the Treasury to establish an Office of Revenue Allocation to arbitrate any claims or disputes among States.

(Sec. 5) Prohibits the authorizing of any appropriations for the Internal Revenue Service after FY 2003. Establishes in the Treasury: (1) an Excise Tax Bureau to administer any excise taxes not repealed by this Act; and (2) a Sales Tax Bureau to administer the national sales tax.

(Sec. 6) Authorizes the Social Security Administration to collect and administer self-employment income and employment taxes beginning in 2001.

(Sec. 7) Sets forth provisions concerning: (1) the self- employment tax; (2) the indexing of social security benefits; (3) compensating payments to individuals on fixed incomes; and (4) the interest rate on tax underpayments and overpayments.

(Sec. 11) Requires a supermajority in the House of Representatives or the Senate to raise rates.