Despite some confusion at the final whistle United will now face Lincoln in the play-off semi-final with the first leg away at Sincil Bank.
Lincoln sneaked above Bury on goal difference, setting up a Lincolnshire derby in the play-offs.
The first leg is scheduled to be played on Saturday May 10, with the second leg the following midweek. The dates have not yet been decided, and the FA could be asked to make the final decision if the two clubs cannot come to an agreement - possible TV coverage could also play a part in deciding the dates.
The prefered dates of United would see the first leg being played on Sunday May 11, with the second leg at Glanford Park on the Wednesday evening.
Iron manager Brian Laws said: "We are absolutely delighted after the the opportunity to go away from home and bring Lincoln back to Glanford Park.
"We are delighted to be fifth in the table, it is going to be fantastic over the next seven days in Lincolnshire."
Rushden And Diamonds secured the third division title with a 1-1 draw against Hartlepool United at Nene Park, while Exeter City were relegated from the Football League after Swansea pulled away from trouble with a win over Hull City.