I am in my mid-40s and would like to take the money from my SEP and put it in my ROTH, which I've had for about seven years.

I realize I pay taxes on the SEP distribution.
Is that my current rate (15%) ?

As long as it doesn't take you above the top of that bracket, yes. Remember that you can choose how much you want to convert. It's not all or nothing.

Are there additional taxes or penalties involved?

No

Will the rollover funds need to sit for five years before I have access to them without penalty or tax?

Kinda, sorta. The law specifies the order in which money comes out of Roths:

1. Contributions
2. Conversions
3. Earnings

You must keep a running journal of what went in and what went out because of this ordering rule.

Contributions come out tax and penalty free.

Conversions come out tax free. If you're under 59 1/2 and it's been less than 5 tax years since the conversion the distribution is subject to the 10% premature distribution penalty. That's 10% of the amount of the conversion that was taxable, so you also need to keep your 8606's from the conversion years.

Earnings are distributed tax and penalty free only for qualified distributions.

See Chapter 2 of Pub 590.

Phil
Rule Your Retirement Home Fool