There was one company that applauded Janet Yellen's hints at rising interest rates last week: Paychex (PAYX). Paychex is an outsourced HR firm that provides 570,000 small and medium-sized businesses with payroll and more specialized HR services. Because of the bevy of tax and compliance issues involved in a small business paying its people, the firm is able to earn profits for its expertise. So why does that make PAYX a winner in a rising rate environment?