The IRS Code states: "We will accept an Offer in Compromise when it is unlikely that we can collect the full amount owed and the amount you offer reasonably reflects the collection potential..." (Internal Revenue Code section 7122).
It may be possible to reduce the taxes you owe - including all penalties and interest - at an enormous discount. There is no preset bottom limit that the IRS will accept to settle your debt especially if your offer is prepared properly. The key is to determine the least amount that the IRS will accept from you before you make the offer.