Any country which has a system of income tax (and as far as I know all countries do) requires you to declare all your income so that tax can be assessed correctly. Failure to do so will count as tax evasion. Each country will have a system of tax allowances which may reduce the amount of tax you pay, but the actual income has to be revealed before the allowances can be claimed.
So for game making, all legitimate expenditure to make the game (e.g. paying for resources, paying for a hosting site) will - in most jurisdictions - be deducted from your income and tax charged on the rest. But there's no getting round the basic requirement to tell the tax authority that you have had some income.
I don't know much about selling games, but having helped hubby with businesses for years, I do know a little bit about small businesses.
Everything is an expense. Keep track of EVERYTHING.
If you use a computer, if you buy resources to try out, obviously the game maker, the table the computer is on, the notebook you write your ideas down on, the meal you eat while discussing your game with a friend (50%), the gas you use driving to a video game store to research what games are popular, your internet service -
These things may not all be 100% deductible, but a good accountant can shield a large portion of your "income" as "expense" rather than "profit." And you only pay taxes on profit.
Tax avoidance is not illegal. Only tax evasion.
If you are serious about making money, you should be serious about paying taxes, and also about keeping good records.
When I was in the hospital I did actually have a nurse that was funny, did all these extra nice things for me and said she liked me. So you know what that means. That will be the last time I'll hear from her.