you can choose to pay 1 lump sump or via giro interest free instalment at the end of the assessment year.

Normally singapore salary is deduct for CPF contribution which eligible for PR and citizen. Other than that, maybe some company got offer charity donation which allow you to make do income tax relief. This donation will be automatic deduct from your salary after you had agree with it during the offer letter signing.

Mid of April is the due date for IRAS filling. You doesn't need to pay at that time. Just wait until the notice of assessment mail it to you. You can opt for full payment or GIRO it monthly.

Anyway, this is what i know from my current and past working company.

those are voluntary donations which must have your consent. I think what he's asking is compulsary deductions.

What role and industry you are looking for?