No. Reason: Taxes are not a contract for specific services, so even if the government did nothing for you in return for your taxes, you do not have recourse to a rebate for "breech of contract." The only recourse is political. Theoretically if the government failed to provide a service that was required by law or Constitution, there could be legal action to force the government to do that action but you still don't get your tax money back.
It might be an interesting act of civil disobedience, but no not legal.
That is the answer. But to address some of the other premises of your question (Note: these are irrelevant because see above answer):
- The U.S. government runs at a deficit anyway, meaning the amount spent each year is more than the amount of revenue collected. For example, in May, 2018 the CBO estimated that for FY2018:
BUDGET PROJECTIONS FOR FY 2018
(As of May 24, 2018 )
DEBT HELD BY THE PUBLIC (End of Fiscal Year)
So even if in the partial shutdown, gov saved 20%, every cent of your taxes would still go to the expenditures; the deficit would just be a little less.
The U.S. government is saving quite a bit of money by not paying some
subset of its employees, etc. .... believe that many of those
employees will not receive back-pay.
Probably not true. In the past modern shutdowns, employees received the back pay, whether they worked as emergency employees or were home. A bill as already been proposed in Congress to ensure that all will be paid when this ends. Some contractors might not get paid because they get paid by their employers, not directly by the gov. So in some cases no work, no pay. There are bills proposed to get them paid also.
Note- I do not at all mean to downplay the effect on people's finances and morale. Missing a paycheck today even if the money will/might come eventually is a real hardship.