Only single wins of $1,200 or over are subject to withholding. If you won over $1,200 in small wins you would not be subject. When you press the cash out button the machine doesn’t know your citizenship and will just print a voucher for whatever you had. Any $1,200 or over win will always lock up the machine until an employee unlocks it. On high denomination games, usually starting at $10 or $25, the casino may keep a log of all your taxable wins. On a $500 machine, I’m sure they would have somebody standing right next to the machine do the paperwork. When you are done they will give you a single W2G form for the sum, and in your case subtract the withholding from that.