出典:Wiktionary
By surface analysis, two + pence, collective plural of penny.
Same for the definition: "Short for tuppence worth (“one’s opinion”)." however, this idiom is derived from this fact; in Britain it used to cost two pence ("tuppence") to post a letter, usually holding one's opinion.
tuppence (countable かつ uncountable, 複数形 tuppences)