It's technically called the high rising terminal, or rising inflection - but you may know it as "sounding Australian". Ending all your sentences as questions? All the time? It really makes you sound unsure of what you're saying?
It's important to sound confident in interviews, and that confidence comes across in how you speak as well as what you say. If you find you're umming, aahing, "like"-ing, speaking with a rising inflection or stopping mid-sentence, you need to drill these habits out through plenty of repetition.
To start with, pick one or two of the most common interview questions and practise answering them out loud. (You can jot down notes on how you will answer first, if you feel happier with notes to hand.) Then practice again, and again, until you feel as though you are reciting a poem or dialogue you know well. Listen to (or record) yourself speaking - any "ums"? Any rising inflection? If so, practice again, focusing specifically on eliminating these. Practice makes perfect.