Since each County has their own way of doing things, here's a nice list of every County Sheriff Department in Minnesota http://stevendiadoo.com/mn-sheriff-departments/
In short, yes, the fund have to be either in cash or in some sort of certified funds. I'm not sure if they would allow a wire, but it's worth checking with whatever county is doing the sheriff's sale. It's my understanding that you must be there in person to purchase, have the funds in cash/certified funds and be prepared that whatever other lien holders are present may be bidding against you. Also, my colleague is correct, there is a 6 month redemption period here in MN, so the original owners will have that time to redeem their status with the property. Your funds will be held in a trust account until that time has expired.