Is it permissible for me to accept the gratuity paid by the client in exchange for completing their transactions, knowing that I do not offer them any special facilitations, and that those who partake in accepting it are considered diligent in prayer and have even been rewarded by the employer?

An employee is entrusted with their work and is obligated to perform it as required in exchange for their salary. They are not permitted to accept gifts from clients in return for special favors. Colleagues should be advised of this. It is permissible to work with them provided that clients are not discriminated against. If something is given without any reciprocation and the employer has authorized it, then there is no harm, though it is preferable to avoid it to prevent any pretense.