The ballots shall be kept in a sealed box; and, at the conclusion of the election, the box shall be turned over forthwith by the managers to the officers designated as the returning officers and shall by them be safely and at once delivered to the mayor or other chief executive officer of such city or town. Within three days after such election the votes shall be canvassed and counted by the board of aldermen or other governing body of such city or town, and it shall declare the result.