The tax is not a special or additional tax. NJ Law requires that non-resident individuals who sell or transfer real property located in New Jersey make a NJ Gross Income Tax estimated tax payment on the gain as a condition of the recording of the deed.
The state Division of Taxation has "amended" their position that, in order to utilize the Resident form, the seller MUST be moving to a New Jersey address as of the date of deed transfer, or they must use the Non-Resident (GIT/REP1) form, thereby requiring them to pay the minimum 2% of the deed consideration directly to the state.
The tax payment is determined by multiplying the gain on the sale by the top NJ tax rate of 8.97%. The payment cannot be less than 2% of the "consideration" received - or gross proceeds from the sale.
This is not an "exit tax", but an estimated tax payment. The purpose is to make sure that the non-resident individual files a Form NR-1040 to report the sale and pay tax on the gain. Because the required estimated Tax payment is made at the highest tax rate, the individual should receive and be entitled to a refund on the NJ-1040.
As others have said earlier, there is a real estate transfer tax involved in the sale. here is a link to FAQ's regarding the tax and who pays: http://www.state.nj.us/treasury/taxation/lpt/rtffaqs.shtml
Also, here is a calculator to figure out how much the tax would be: http://www.state.nj.us/treasury/taxation/lpt/rtffaqs.shtml
If I may be of further help, don't hesitate to contact me directly.