Herrmann, who played in seven games with the Twins last year as a September callup, hit .100 in eight Grapefruit League games. The 25-year-old will be used as a catcher and part-time outfielder at Rochester.
"He's got some work to do," Twins general manager Terry Ryan said. "He can play some left field, which he did in the Minor Leagues, which gives him a better avenue to get up here, and he can certainly catch. He's very athletic, but he just needs to go down and get at-bats. I was hoping he'd come here and really have some success and give us some thoughts because of his versatility, but he still has some work to do."
Pinto, 23, had a breakout season in 2012, hitting a combined .295/.362/.482 at Class A Advanced Fort Myers and Double-A New Britain, but he hit just .182 this spring.
Santana, 22, was impressive this spring, showing off his range at shortstop while hitting .333 with a .528 on-base percentage in nine games. Santana, the club's No. 12 prospect according to MLB.com, hit .286 with eight homers, 21 doubles and eight homers at Class A Fort Myers last year.
"He's a legitimate shortstop candidate of the future," Ryan said earlier this spring. "He's got all kinds of ability and athleticism. Now it's just a matter of consistency. He can do about anything."
Hermsen, 23, struggled in his first big league camp. The club's Minor League Pitcher of the Year for 2012 had a 13.50 ERA in 2 2/3 innings and was also hit hard in a "B" game and an intrasquad game.
May, who was acquired in the Ben Revere trade, gave up one run on two hits in 3 1/3 innings this spring. The 23-year-old is headed back to Double-A, where he had a 4.87 ERA last year with 151 strikeouts and 78 walks in 149 2/3 innings.
"He's got all of the things we're looking for in a starting-pitching candidate," Ryan said. "He's got size, he's got arm strength, he can spin a ball, he's a good kid and a good worker. Now it's just a matter of him attacking the strike zone."
Tonkin, meanwhile, threw four scoreless innings with two strikeouts and impressed manager Ron Gardenhire along the way. The 23-year-old struck out 97 in 69 1/3 innings with a 2.08 ERA at Class A Beloit and Fort Myers last year.
"We like the kid an awful lot," Gardenhire said earlier this spring. "We'll have to wait and see as we go along. He just throws the ball, he lets it fly, he's got a great power sinker, good velocity. Last year, he set himself up and became one of our prominent prospects in our eyes, and he's moving ahead."
Ryan, though, said just because the players were assigned to certain levels doesn't necessarily mean that's where they'll end up to start the season. He said players could be moved up depending on how they fare in Minor League camp, as they're usually conservative with where they assign players.
"That's just where we assigned them, so don't get too carried away with that," Ryan said. "They can move up or down depending on how they do over there. We always like to send a guy where we think they belong but they have an opportunity to get out of there."