As nice as ninepence
Neat, tidy, well-ordered.
The variants, 'as right as ninepence' and 'as neat as ninepence' are just as common as the 'nice' version (also, less commonly, 'as clean as ninepence' and 'as grand as ninepence') and it isn't clear which came first.
There are suggestions that this expression derives from from 'as nice as ninepins'. In the game of Ninepins (Skittles) the pins are set out in a square. For the game to be fair this must be done neatly and accurately or, in the old parlance, nicely. That derivation is attractive but seems unlikely, as there is no early records of 'as nice as ninepins' in print, which we might expect if the 'ninepence' version derived from it. The 'ninepins' form, in the guise of 'as smart as ninepins' isn't found until the 20th century, so it is reasonable to assume that it is a simple mishearing of the earlier 'as neat/clean/grand as ninepence' versions.
The earliest known recorded form of the phrase is 'as neat as ninepence'; the first citation is in James Howell's English Proverbs, 1659:
"As fine as fippence, as neat as nine pence."
The 'fippence' (five pence) here makes it clear that the reference is to money rather than to skittles. For it to appear in a list of sayings viewed as proverbial it must have been in existence for some time before 1659. There was a ninepence coin in circulation in the 16th and 17th centuries, although there was nothing especially neat or nice about it. The rhyming and alliterative style of the citation suggests that the 'neat' and 'nice' were chosen just for that reason.
The form 'as nice as ninepence' didn't arise until recently, in the late 20th century.
See other 'as x as y similes'.