Dog walking. Does it requires reporting?

I'm planning to do occasional dog walking. If I receive some cash for occasional dog walking, do I need to report it?

 

I found here, https://www.irs.gov/individuals/check-if-you-need-to-file-a-tax-return,  that if I receive less than $400 I don't need to file it, but if I'm filing it because I have another job, should I include the dog walking earning even if the value is for example only $100?

 

I don't have a business open, do I need to have one to receive cash for occasional walks?

 

Thanks.