Until you get audited. In the end you will have to give them more because of interest and fees. Why risk it?
Discussion
Slave
In an IRS audit, the burden of proof is on you. That means they can make a claim on your wealth, and it's on you to prove otherwise. If your transaction history is complex then it becomes even harder to prove. After the audit is over and the IRS determines that you owe them (typically an arbitrarily large amount) and you don't pay them then you go to jail.