Rulings on contributing to voluntary provident/retirement fund possibly based on interest

I am working in a private company. According to my company's policy, it is mandatory to contribute 3% of my salary to the Provident Fund. However, if an employee wishes, they can contribute up to a maximum of 15%. The government of the country exempts the contributed amount from income tax. Because of this benefit, I contribute 15% of my salary to the Provident Fund. As per the rules, the company also contributes an additional 3% on my behalf. Notably, the company's contribution is fixed and does not depend on whether I contribute more or less. This total of 18% is invested in various businesses and banks, but I do not have access to detailed information about these investments. I also do not have the option to withdraw this money immediately. Upon retirement, the company will provide me with the full amount, including any profits generated from the investments. I intend to donate the profit without expecting any spiritual reward. In this situation, I have two questions: 1. Is it permissible for me to contribute more than the mandatory 3% with the intention of benefiting from the tax exemption? 2. Is it permissible for me to accept the 3% contribution made by the company in the future?