Also they could've gotten a tip from China: their 5 fen (.0066 USD) coin is made out of aluminum, and the weirdest coin I've ever seen.
That sounds like an extremely malleable coin O_o
I can't say for the 5 分 coins since I've only ever seen the 1 or 2 versions, but they're not malleable, just very thin and ugly. That said they are worthless even in China, the only time I ever get them is due to a bizarre system for paying my rent that means I get 2 fen change every month. In day to day transactions you
never use them, all prices are rounded to the nearest mao (10 fen).