is this the answer?
"The penalty for failing to file on time is five percent per month of the balance owed. If a taxpayer files more than 60 days late, the minimum penalty is $100 or the balance due, whichever is less. The penalty for paying late is 0.5 percent per month of the balance owed. This rate drops to 0.25 percent per month for a taxpayer who files on time and enters into an installment agreement with the IRS to pay the balance owed. There is no late filing penalty on a refund return, but a taxpayer who fails to claim a refund within three years of the filing deadline generally loses the right to that refund."
So from reading that, if you pay all your taxes on time, and say you even paid $1 extra, if you file late you won't get a penalty. However, if you fail to claim your refund within 3 years, you probably won't get it.