While many entrepreneurs remain cautious and continue to rely on contract workers, small businesses showed a slight increase in hiring in May, according to SurePayroll's Small Business Scorecard.

The average size of small businesses increased in May by 0.3 percent, while salary per paycheck dropped by 0.1 percent, AOL Small Business reported.

Average small-business size has increased 3.7 percent year-to-date, and salary per paycheck has ticked up 0.2 percent, representing an overall boost in hiring and salaries in 2010.

Despite the continued growth, small-business owners polled were slightly less optimistic in May. Optimism in the economy dropped to 63 percent, from 67 percent in April.

SurePayroll, a Glenview, Ill.-based online payroll provider, analyzes payroll data from tens of thousands of small businesses each month.