Each county auditor and tax collector shall annually file with the board of supervisors of his county itemized statements showing the additional expense to his office caused by performance of the duties imposed upon him by this article. Upon the filing of such statements the board of supervisors, by an order upon its minutes, shall deduct such expenses from the tax money of the district while in the hands of the tax collector and transfer the amount deducted into the county salary fund. Not more than one-half of 1 percent on the amount collected shall be so charged or deducted by any county.