Section 16. That it shall be the duty of the register of wills in the several counties of this commonwealth, to collect and pay into the state treasury all taxes due, and that may be due, under the collateral inheritance laws of this commonwealth, of which he shall make a return under oath to the auditor general; and he shall be allowed to retain five per centum on all taxes paid and accounted for in full, for his services in collecting and paying over the same.