Is there a list of plural names of currencies?
Wiktionary has a category for everything, including one for currencies, with currently 289 entries.
Invariant plurals:
- Yen (Japan)
- Sen (fraction of a yen, Japan)
- Yuan (China)
- Jiao (fraction of a yuan, China)
- Fen (fraction of a jiao, China)
- Baht (Thailand)
- Satang (fraction of a baht, Thailand)
- Rand (South Africa)
- Quid (British slang)
Irregular plurals:
- Penny / pence (fraction of a pound, United Kindom only)
- Paisa / paise (fraction of a rupee in India and Pakistan)
- Drachma / drachmae or drachmas (Greece, formerly)
- Krona / kronor (Sweden)
- Krone / kroner (Norway and Denmark)
- Markka / Markkaa (Finland, formerly)
- Lira / lire (Italy, formerly)
- Real / reais (Brazil)
Regular plurals:
- Dollar / dollars
- Euro / euros
- Cent / cents (fraction of a dollar or euro)
- Penny / pennies (Canada and United States)
- Pound / pounds
- Franc / Francs (France formerly and still in parts of Africa)
- Centime / Centimes (fraction of a franc)
- Rupee / rupees (India and Pakistan)
- Dinar / dinars (with dihram, several states in the Middle East and North Africa)
- Dihram / dihrams
- Ruble / rubles (Russia and other former SSRs)
- Peso / pesos (Mexico and several Latin American countries)
- Bitcoin / bitcoins (no comment)
- Loonie / loonies (Canadian slang)
Of course there are many, many other named coins and currencies. Some of which, yes, may be irregular. However, the anglicized standard pluralization (stick an 's' on it, basically) is accepted in most cases.
A simpler approach could be to check the dictionary as and when the need arises for an individual currency-name; e.g.,
lev (lf) n. pl. lev·a (lv) (TFD)
Take off from the TFD Currency Table: Listed by Country, look up the currency against the country, say if the currency is lev, click on it to go to the respective definition page. Alternately, use the Currency Table: Listed by Basic Unit (Bold) and Subunit, on the same page.
The default plural, of course, is the usual +s, so if the definition page does not expressly show a plural, you know.