You MUST file if your income is more than $10,350 and you are single and not a dependent, or more than $6300 and you are single and someone else's dependent. There are other limits for different filing statuses, and your state may have different limits as well. See the link provided above.
The IRS does not necessarily know that you are only due a $2 refund. If you do not file, they will create a substitute tax return in their system using information sent to them by banks and employers. But, they are not obliged to give you credit for any deductions, credits or dependents, so the substitute return could very well show you owing tax, which they will bill you for.
The real purpose of a tax return is to get all your income and deductions on official record. Whether you get a refund or not is almost a side-effect.
