What should I do with the small surplus of money remaining after distributing salaries, knowing that I am not the accountant, and I have asked all employees and the accountant and no one reported any shortage?

The money must be returned to the institution from which it was received. If they refuse to take it, it should be given as charity with the intention that the reward goes to its owner. If the owner is known, they should be informed of what was done. If they approve, then that is sufficient. Otherwise, the charity becomes yours, and you remain responsible for the money.