You see a $1 bill on the sidewalk. Is it 'worth' it to pick it up, because of all the paperwork you need to file to the IRS?

This is basically what you're asking with the small transactions. The IRS doesn't care. You get $50 in your birthday card, you earn $20 baby sitting, $20 mowing someone's lawn, $20 shoveling driveways, etc. The IRS doesn't care.

If you win $1000 in a slot machine - the IRS cares. You pay $20,000 cash for a car. The IRS will be all over that.