A first-half treble from Tyler Beck set Steven Frederiksen's Cayton side on their way to victory at the Flamingo Land Stadium.
Top scorer Si Coupland then took his league tally to 34 for the campaign with a hat-trick and Ryan Jones also got his name on the scoresheet in a comfortable win.
Roscoes' goal came courtesy of Liam Rowley, who tapped in at the back post from a pin-point Craig Spooner cross.
Andy Noon was Bar's man of the match.
Player-boss Frederiksen said: "Tyler Beck and Nicko Dunn were outstanding and shared the man of the match award.
"We were fully in control first half, started the second half sloppy and let Roscoes have a few chances, but after a few changes we were back on control and for a comfortable win."
Frederiksen is delighted to have wrapped up promotion to the top flight.
"We're relieved to take second spot and secure promotion after missing out on the title," he added.
"Our target all along was to get promotion, we've got a strong, committed squad made up of a great set of lads both on and off the field.
"We really want to go out now and challenge the Angels and Trafalgars.
"I can't thank the lads enough for their commitment this season so far, they've been a pleasure to manage."
Trafalgar cruised to a 7-0 win against Valley in Division One.
Traf had to be patient as they only led 2-0 at the break, but they dominated second-half proceedings to take a comfortable win.
Steve Smith smashed in a hat-trick for Traf, whose other goals came from player-boss Joel Ramm, Jack Ramos, Sam Pickard and a stunning long-range strike from Frank Belt.
Valley had their moments in the contest, with Dan Maw firing against the bar late on.
Michael Hernandez and Danny Appleby stood out for Ben Kristiansen's side.
"I'd like to say a massive thank you to all my lads for an incredible first season in Division One," said Kristiansen.
DIVISION 1: Valley 0-7 Trafalgar
DIVISION 2: Roscoes 1-7 Cayton