How is the cost of using DocumentDB calculated?

Question

NoSQL

Good evening. Interested in the question of how the calculation of the cost of using the NoSQL database DocumentDB in Microsoft Azure. The cost calculator has a "number of collections" field, by which, in fact, the total cost is multiplied. + as I understand it, the prices for 10GB (2 rubles / hour) are indicated in the tariffs. So, if I have, say, not one collection of 10GB, but 50 collections of 200MB each, what will be the final check? 2 rub/hour or taking into account the number of collections: 100 rub/hour?
And another question: if I take, say, not 10GB, but 1GB, does this affect the final cost of services or are they rounded up?
Interested in the answers of those who have already used this service.