I don't know how Zimbabwean citizens will react to such a law, but if you ask me, it's not really right and proper.
Gamblers place bets every single day, and they lose money in almost all their bets, and when they manage to win a little bet, which, if you check very well, out of all that they have wagered in the past, that winning can't amount to it, yet the government will want them to report such winning and remit some percentage of that amount to them as tax.
This is just daylight robbery when they can tax the gambling industry themselves for each money spent on their platform by their citizens and leave those gamblers out of this because this money will still, in one way or the other, come back to their economy.
Why is it the government's business if their citizens are losing money in gambling? Although I also don't like taxes, 10% doesn't seem too much; it's up to 15% here, and it only applies for withdrawals above €100. What you've said doesn't make any sense. Governments want to make money out of an extremely profitable industry; what happens with the taxation money is something that I do not and can't know. If it's put to good use, I don't think it's too much of a problem. Gambling should be considered a privilege, a luxury; if you can afford risking your money, you can afford a small percentage of it going for taxation. I'm not implying that you should like it, but I personally find it reasonable.