Doncaster threatened inside the opening couple of minutes as Martin Woods saw his low angled shot parried by Mark Howard while the United 'keeper also kept out Chris Brown's follow-up.
United striker Richard Cresswell fired over from inside the area before Paul Gallagher tested Gary Woods with a 25-yard effort which the visiting keeper turned over the bar, with Harry Maguire seeing a header blocked following a corner.
United's Nick Blackman sent a free-kick off target in the second half while, at the opposite end, Howard made a comfortable save after Jamie McCombe had met Martin Woods' cross with a downward header.
Blades boss Danny Wilson sent on recent recruit Dave Kitson for his debut in a bid to spark some life into the home side's attack but the former Reading marksman was unable to make an impression.
