The ultimate power to determine how much the governmen twill tax and spend, and what it will spend tax dollars for, lies with:

U.S. Congress

Explanation:

The ultimate power to determine how much the government will tax and spend, and what it will spend tax dollars for, lies with UNITED STATES CONGRESS.

The above statement is true according to the United States, Article I, Section 8 of the Constitution, which state that "The Congress shall have the power to lay and collect Taxes, Duties, Imposts, and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts, and Excises shall be uniform throughout the United States;..."