From what I understand based on multiple forum posts (as it has not affected me), many sellers get Brazil added as part of the "Unified North America" account, which includes US, Canada, and Mexico (obviously someone failed geography in school).

As such, it's part of the $39.99 fee charged for the NA account, so no extra charges. However, if it works like Canada and Mexico, the monthly charge will be broken down between the various countries, sometimes resulting in small charges to your credit card, but they should total $39.99, plus or minus a small amount due to exchange rate fluctuations.

You should put Brazil (as well as Mexico and Canada, if you don't want to sell there) on Vacation Mode; this will not affect your US (.com) store. Once you do that, no one will be able to purchase from you on those sites.

Additionally, to avoid having the separate charges, make sure that you have no inventory in those countries in which you don't wish to sell; you do this by using the drop-down at the top of seller central to switch country, and delete any listings in Manage All Inventory (DOUBLE CHECK WHICH COUNTRY YOU ARE ON BEFORE DELETING!! There is no "undo" if you delete the wrong country).

I have heard reports from VERY experienced sellers running into issues when even just asking about closing other country accounts; hopefully your innocent question has not triggered a problem. Just put the store on Vacation, check the inventory, then don't worry about it.