There's never a tax deduction in this case. If you make only non-deductible contributions to a traditional IRA (and you have no other traditional IRA accounts at other institutions), then you can convert the traditional IRA to a Roth IRA. You do not pay tax on the contributions (since you already paid tax on them) but you do pay tax on any income (growth) in the account. For that reason, most people do the two steps pretty close to each other, to minimize the amount of taxable growth in the traditional IRA.
