GTA 5 Online might have micro-transactions. Reddit user 1880 discovered that when you open the store section in the pause menu of GTA V it requests an XML document that contains item listings and descriptions.
The file contains items that you would expect to be sold digitally like a collectors edition upgrade but in addition to those, there are listings for cash cards of varied values.
The descriptions of these items tell the whole story, one of the descriptions written there says "Cash is king in this town. Solve your money problems and help get you what you want across Los Santos and Blaine County with the purchase of cash packs for Grand Theft Auto Online."
Supposedly this is only for GTA Online and not for GTA V. This all kind of makes sense since, Rockstar would not build a huge on-going multiplayer service without some way to earn money from it.
Additional players have had a hard time earning the amount of money needed to buy high end residencies in the game, unless you used hacks or cheats, so, maybe thats why Rockstar will encourage additional sales.
This is not big of a surprise since every Ammu-Nation has a button link to go to the Xbox store or PSN, but there is nothing there yet.
Another question which pops up is : will these additional purchases make the game pay-to-win? Will you be able to buy better weapons, better cars and things that will make you better in the game? Or is it just stuff that will make your character look better in game, like clothes, hats, shoes and etc.?
Keep in mind none of this is confirmed as of yet. It might have been added in early development and they have forgotten about it.