“Soit” is a form of “être”, aka “to be” like in “que la lumière soit” (“Let there be light”). In the form you describe in your first example sentence, it could be replaced by “which is” or any other synonym like “i.e.”, “which is equivalent to”, “aka” …

Environ 10 milliards de roupies népalaises, soit l’équivalent de $135 millions doivent encore être échangées.

In the phrase above soit is the third person singular subjunctive of être (to be).

For further details please refer to Understand soit

If you wanna understand the French Subjunctive

Soit here isn’t a verb but a conjunction, and you could translate it with “or” in this context, or a more verbose “that is to say”.

It’s related to its usage as a conjunction for closed lists of alternatives: “Soit c’est toi qui le fait, soit nous, soit elle”, which also overlaps with English’s “or”.

It’s used to expand on the meaning of the preceding clause, to give it an alternative explanation. The conversion of currencies and units is where you’ll see it most, or a summation of a list:

• Ce voyage lui a coûté 789 000¥, soit 6 323,79€ (this trip cost them 789,000¥, or 6,323.79€)

• L’armée rassemblait 2 500 mercenaires lorrains, 4 000 troupes régulières et une levée de quelques 3 400 locaux, soit la moitié des forces disponibles aux opposants du comte. (The army counted 2,500 mercenaries from Lorraine, 4,000 regulars and a levy of some 3 400 local inhabitants, that is to say around half of the forces available to the enemies of the count)