What I can say is that, when the payout program started, all payout requests did go through a manual process (the minimum rate was the same then, by the way). Later on, there is evidence of account "snapshots", which is used to track income made before and after Roblox bumped the exchange rate up [1], which is described with some detail [2]. So it's not unlikely that there are other kinds of counters keeping track of income sources. Even so, there is still evidence for some sort of manual processing, at least up to last December [3].

[1]: https://devforum.roblox.com/t/the-robux-exchange-rate-and-mo... [2]: https://devforum.roblox.com/t/the-robux-exchange-rate-and-mo... [3]: https://devforum.roblox.com/t/holiday-schedule-for-the-devex...