Tax software is an especially interactive way to dispense tax advice. Several years ago, the IRS enlisted a few tax-software companies, including TurboTax and CompleteTax, to offer free filing of federal returns for people with adjusted gross income below a certain amount. This year, the cutoff is $58,000, which would allow about 70 percent of all taxpayers to file for free. Taxpayers in that category can choose to file using one of 17 companies listed on the IRS’s website. In most cases, however, taxpayers cannot use the software to file state tax returns for free.