The contribution which shall be paid by the employer to the Fund shall be six and a quarter per cent of the basic wages, dearness allowance and retaining allowance (if any) for the time being payable to each of the employees (whether employed by him directly or by or through a contractor), and the employees ' contribution shall be equal to the contribution payable by the employer in respect of him and may, if any employee so desires and if the Scheme makes provision therefor, be an amount not exceeding eight and one third per cent, of his basic wages, dearness allowance and retaining allowance (if any); Provided that in its application to any establishment or class of establishments which the Central Government, after making such enquiry as it deems fit, may by notification in the Official Gazette specify this section shall be subject to the modification that for the words "six and a quarter per cent," the words "eight per cent" shall be substituted: Provided further that where the amount of any contribution payable under this involves a fraction of a rupee, the Scheme may provide for the rounding off of such fraction to the nearest rupee, half of a rupee or quarter of a rupee.