Dec 1 (Reuters) - U.S. Treasury Secretary Janet Yellen said on Wednesday that she agreed that allowing state-legal cash-only cannabis businesses to access the U.S. banking system would allow the Internal Revenue Service to improve collection of taxes. Representative Ed Perlmutter of Colorado asked Yellen during a U.S. House Financial Services Committee hearing whether allowing cannabis businesses to access the banking system -- now prohibited by federal law -- to conduct transactions would make the IRS" job easier in collecting tens of millions of taxes that have gone unpaid from such firms. "Yes, of course it would," Yellen replied.