Starting next year, casinos and card rooms must withhold 25 percent of winnings over $5,000 for anticipated tax payments.The IRS released a new procedure this week, which will apply to payments made on or after March 4, 2008. The $5,000 figure applies to a gambler's profit, Part Time Poker News explained. "If you entered a tournament with a buy-in of $10,000 and cashed for $12,000, you'd be fine with a net win of $2,000.