Singapore dollar is not real money, its legal tender (says so on the note) that like most paper currencies are attached to the US dollar.
Eventually all paper currencies not backed by a hard stabilizing asset like gold (hard to dig out and process, hence a stable measure of value) will go to zero.
It will go to zero even faster in war time like the Japanese banana note.
You have to wonder why they use plastic over paper for $2,$5 and $10 denominations. Maybe because our money is getting less and less of value of being printed on good quality paper that it now has to be mass printed on cheaper plastic?
Smaller the denomination = larger the number of notes for that denomination.
Look up Mike Maloney's 'Hidden Secrets of Money' on Youtube. Knowledge is Power.