According to tax expert and former IRS attorney Sandy Botkin, you should never use cents in figuring out your tax return. "Always round," says Botkin. "Mathematical errors cause some of the biggest scrutiny of your tax return because things don't match up. If you use cents, you're just increasing your chance of making an error.
"If you do your own tax return, for the most part, you increase your chance of being selected for an audit. The IRS figures if you do your own return, you don't know what you're doing, unlike accountants who might do hundreds of returns. People tend to make more mathematical mistakes when they do their own returns than accountants make."
Source: "Tax Expert Sandy Botkin"