This question may seem tricky, but it’s actually fairly simple to answer. The hiring manager asks this question to figure out if you’re going to use the company as a stepping-stone, or if you have long terms plans.
No one really expects you to have a 5-10 year plan. Your answer should follow these parameters:
You hope to increase your skills and learn more about the industry.
You aren’t sure exactly where you’ll be in 5 years, but you’d like to have worked your way up into a management position.
Avoid saying that you do not know the answer.