Tuppence meant two pennies, and now means two pence. I still use tuppeny bits
I agree that a woman's tuppence is her "front bottom", and is usually used in a sexually derogative way. (The alternative word "minge" was merely anatomical). I have no idea if its rhyming slang.
As a child in east London I found the song "Feed the Birds" hilarious. Mummy (Irish) loved it and did not know why Daddy hated it nor why her children found it hilarious when she sang it in his absence. Similarly Daddy refused to allow us to watch the TV series featuring Agatha Christie's husband and wife sleuths "Tommy and Tuppence". I'm guessing that as Mummy, Walt Disney, Agatha Christie and my other half (parents from West London, raised in various locations across Europe) and the Online Oxford English Dicitonary do not know the "front bottom" meaning, its geographical spread is limited.
The word also crops up in some respectable idioms, where it generally means worthless. "I don't give tuppence" (roughly speaking, "I don't care")
"its not worth tuppence" or "I wouldn't give tuppence for it" (its worthless).
Truppenny bits (as well as being rhyming slang for tits) were coins worth three pence, which as I recall had 5 sides. They unfortunately disappeared at decimilisation. I was outraged. My sweetie money changed from a thruppeny bit a week to tuppence. I eventually managed to negotiate a raise to a bob (five pence), but I still miss truppeny bits.