If your business is incorporated and you are selling out to a larger corporation, it may be possible to defer any tax due on the sale. How? By structuring the sale as a corporate reorganization, and accepting the purchaser's stock in exchange for your own business's stock. If you manage to comply with the IRS's extensive rules for these types of transactions, you won't be taxed on the value of the stock you receive, until you sell it at some point down the road. If you receive other property or tax in addition, however, you'll have to recognize taxable gain to the extent of this "boot."
This type of deal is only advantageous if you are selling out to a buyer whose stock is a good investment. Remember, you'll be exchanging a nondiversified investment over which you had control (your own company) for a nondiversified investment over which you may have little or no control. Under Federal tax laws, you generally can't go out and immediately sell the buyer's stock; you may be required to hold it for as long as two years, or you will lose the tax-free status of the transaction. In two years, almost anything can happen to the value of the stock.
If your buyer proposes structuring the deal as a merger or corporate reorganization, our advice is that you seek the advice of an attorney with extensive experience in this very complicated area.