From what I understand you do have to declare your winnings, BUT, you should keep up with what you lose, too! You can offset your winnings by your losings!
In Arkansas (and probably in other states) you can register as a "professional gambler" with the IRS, even though gambling here (and maybe where you live) is illegal.
You just have to keep up with what you lose and what you win.
i.e., if you've lost $2000.00 on blackjack and won $3000.00, all you pay taxes on is the $1000.00, IF you have proof! You have to request receipts.
This is from my experience with my "Boss" of quite a few years ago.
If it is not correct now, please let me know!