The state of Missouri and all its political subdivisions or instrumentalities shall deduct from the wages and salaries of their employees the amount of any municipal earnings tax levied upon the income of the particular employee, and pay same to the municipality levying said tax. The state of Missouri and its political subdivisions and instrumentalities shall be entitled to deduct and retain of the total amount so collected to compensate such employer for collecting the tax a percentage as follows: Three percent if said municipal earnings tax is one-half of one percent of gross earnings. One and one-half percent if said municipal earnings tax is one percent of gross earnings.