At the moment, Money SE has tag rub-ruble without synonyms and with the following description:
This tag is to be used for the Ruble currency as used by Russia, Belarus, and the state of Transnistrian.
However, RUB is the ISO 4217 code for the Russian ruble, not for the Belarusian ruble (BYN). Hence, the tag name and its description do not match. Lastly, "Transnistria", not "Transnistrian".