The Internal Revenue Service announced yesterday it has reached agreements with Discover, MasterCard and American Express to accept credit cards for federal taxes. Beginning in 1999, U.S. taxpayers will be able to pay IRS bills either by calling a toll-free number or filing electronically. San Ramon, CA-based US Audiotex will handle the phone service. Discover cardholders will be able to use Intuit's 'TurboTax' or 'MacInTax'  tax preparation software to file their returns electronically and then pay using any NOVUS-issued card. A convenience fee, based on the size of the transaction, will be charged regardless of what option the taxpayer uses. VISA has not joined the acceptance group yet, reportedly holding out for a flat fee instead of a percentage of the transaction.