What happens if you earned like 100 dollar from one affialte network and ignore the tax? How will your country know you have to pay tax from that 100 dollar?
Normally you will get a fine, possibly a criminal record and a small chance of jail (though given the scale, obviously unlikely unless you have other criminal convictions already) How they know will depend on your country. Most countries do random spot checks so they gain the records of all your bank accounts etc and ask for explanations for anything that doesn't add up to your declarations. Some are random, some are targeted.
Check your countries tax laws. In the us I think if it is under $500-600 then you do not have to file for taxes, but even so even our tax system is behind, even if you did not pay on a small amount, it could take years for the tax system to catch up... if it is a small amount then I doubt they would do much, if you owed a lot then you can expect them to take more action against you. I doubt they are going to put you in jail because you failed to report taxes on $100 - but check your countries tax laws....
Well, whether or not your country will ever know is kinda beside the point. And sooner or later they'll probably find out--even if it's 10 or 20 years down the road & you could get into serious trouble. I'd just declare it & pay the taxes.