Deductions & credits

Hello,

As a retired IRS Revenue Agent you may know the answer to the following question. 

Say, IRS audits a person and finds that a person does not have the receipts of the house renovations.  Of course, the number a person puts in their tax return is changed and the capital gains are due.  That is clear.  

What other penalties (if any) IRS imposes on the tax return lacking the receipts of the house renovations?

Thank you in advance.