There are about 30 countries that share the same currency name “Dollar” (USA, Canada, Australia, New Zealand, Brunei, Singapore, Barbados, Fiji, Cayman Islands & etc.). but they are not related to each other besides their name, since they have different values from one another, even though they share the same currency symbol: only thing that distinguishes them apart is the country prefix tied to $ (like US$, AU$, NZ$, C$, CI$, FJ$, SG$, Bds$, JA$, B$, etc.).
Colonialism, “$” is a derivative of the shorthand for peso which was the name for the Spanish dollar. So all the locals were calling their money a dollar before the actual “dollar” currencies became a thing.