Honest, not roguish. A square cove, i.e. a man who does not steal, or get his living by dishonest means.
Definition taken from The 1811 Dictionary of the Vulgar Tongue, originally by Francis Grose.
Squab * Square ToesNathan Bailey's 1736 Dictionary of canting and thieving slang
John S. Farmer's collection of canting songs and slang rhymes