Mich. Comp. Laws § 207.530
The tax imposed under this act shall be collected by the county treasurer and deposited with the treasurer as provided in this section. By the fifteenth day of each month, the county treasurer shall, on a form prescribed by the treasurer, itemize the tax collected the preceding month and transmit the form and the tax collected to the treasurer. The county treasurer may retain the interest earned on the money collected pursuant to this act while held by the county treasurer, as reimbursement for the costs incurred by the county in collecting and transmitting the tax imposed by this act. The money retained by the county treasurer under this section shall be deposited in the treasury of the county where the tax is collected to the credit of the general fund.
MCL 207.530