'Smiling rhino' is indeed a curious phrase. 'Shining rhino' might make more sense but both the 1802 Newry text and an undated chapbook printed in Dublin (now in the National Library of Scotland) definitely have 'Smiling'.

'Rhino' is of course a slang term for money, dating back to the seventeenth century. For a discussion on its etymology there is an excellent article on the World Wide Words site:
Rhino. This also mentions the phrase 'ready rhino' (which is a bit of a tautology).