The truth is, yes casinos can control a slot machine or rig it only to give players small wins. Some casinos work with developers to create exclusive games. This gives them even more access to a game's code and RNG.
By law, gambling winners must report all of their winnings on their federal income tax returns. Depending on the amount of your winnings, you may receive the Form W-2G which reports the amount of your winnings and the amount of tax that was withheld, if any.