During an IRS audit, Ms. H provided the revenue agent with a meticulous set of re-cords substantiating every number on the return. The agent actually complimented her on the quality of her preparation. Nevertheless, Ms. H did make an error in her favor. When she received formal notification that she owed an additional $4,350 tax, she was dismayed that the IRS also billed her for $920 interest on the deficiency. She doesn’t understand why she must pay interest when she obviously made a good faith effort to comply with the tax law. Can you explain why?