If the IRS levies your retirement account to pay the back taxes, then there won't be the 10% early withdrawal penalty. You cannot just take it out early yourself to pay them. If you approach them and ask them to take it out, then they might do so and only then, you won't be additionally penalized.
However, if the OIC has not been accepted yet, it may open the door for them to take the entire tax liability.
Look at 5.11.63 in the following link for further guidance from the IRS regarding the matter. Levying from Retirement
