According to current laws, you need to pay taxes on all your gambling wins, regardless of the size. The federal tax on gambling winnings is 25%, while the state tax in Michigan is 4.25%.
When it comes to online casinos, the operators will only withhold federal taxes on winnings exceeding $5000. Smaller wins are paid to you and you are responsible for the taxes.
As for the state tax, online casinos will not withhold it regardless of the size of the win and it is entirely your responsibility to report it.