We don't pay taxes when we gamble in my country, but some other countries closest to our border do pay taxes, even on items they purchased online, but not here in my country.
So if you want the best guidelines you should reveal your country name, it is really a shame that the government want some cut from gamblers risked and win money, what will they do for gamblers when they lose money? I guess nothing, and this makes it so unfair.
I am not sure if it's called greediness on why some governments are like that but maybe their country is also poor and they use the tax to improved it? So, we must be mature enough to accept it especially if we are winning huge. It's only odd if even if we lose we are still get taxed.