Most interviewers are going to stop pushing at this point. But if an interviewer insists, you'll need to decide whether you're willing to hold firm (and potentially risk losing the job opportunity over it) or if you'll give in. If you're in a situation where you have plentiful options, you might decide that you're not interested in working for an employer who would reject you for not disclosing your personal finances. But if you don't feel you have many options, then you might decide that – annoying as this is – you're going to play along. But with most interviewers, it shouldn't come to that point.