A ROTH IRA contribution is not deductible, so that kind of contribution would have no effect on your tax. Only a deductible contribution to a Traditional IRA would reduce your tax. Such a contribution would reduce your tax by, at most, the amount of the contribution times your marginal tax rate. For example, if you are in the 25% marginal tax bracket, a $1,000 contribution would reduce your tax by at most $250.
