Do not use Form 8606 (PDF), Nondeductible IRAs, to report nondeductible Roth IRA contributions.

However, you should use Form 8606 to report amounts that you converted from a traditional IRA, a SEP, or Simple IRA to a Roth IRA.

An individual can make traditional IRA contributions to a SEP-IRA and contributions to a Roth IRA.  However, like other traditional IRA contributions, traditional IRA contributions that are made to a SEP IRA reduce the amount that the individual can contribute to a Roth IRA.  

An employer that has established a SEP can also make SEP contributions to a SEP IRA on behalf of an individual that is an employee of the employer and those contributions do not reduce the amount that the individual can contribute to a traditional IRA or Roth IRA (a self-employed individual can make such SEP contributions without reducing the amount that the individual can contribute to a traditional IRA or Roth IRA).

It is important to remember that:

Review Chapter 2 of Publication 590, Individual Retirement Arrangements (IRAs), for the requirements to contribute to a SEP and a Roth IRA.