If you are talking about federal income taxes, they are never deductible. If you paid state income taxes for 2014 when you filed your return in 2015, the additional taxes you paid with your return become deductible when you file your 2015 federal income tax return (assuming you itemize deductions).
A revenue ruling is the Commissioner’s “official interpretation of the interpretation of the law” and generally is binding on revenue agents and other IRS officials. Taxpayers generally may rely on published revenue rulings in determining the tax treatment of their own transactions that arise out of similar facts and circumstances.