This type of question is seeing the extent of your ambition. Be careful when answering this question not to make it seem as though this job is a stepping stone in your career (even if it is). For example, if you are applying for an accounting job at an accounting firm, don’t tell the interviewer that your long term goal is to work at an investment bank. This is not what the interviewer is going to want to hear. The last thing an employer wants to do is employ you, train you and then see you leave the firm. The best answer you can offer is to demonstrate that your 5 year goals are suitable and match the position you are applying for.