I don't know of such a calculator. However, the calculations depend a great deal on what your tax rate is now, what it will be in retirement and what you do with the funds if not invested in a Roth.

Bottom line is, if you found such a calculator, you wouldn't want to trust the recommendations from it unless you clearly understood what assumptions have been made.

You are best off to make your own analysis--in a spreadsheet program--based on the investments available to you, your exectations for them, and your estimates of tax rates in the future. Then at least you know what assumptions were made in reaching those conclusions.