You can if you cup your hands over your mouth, breathe out through your mouth and then breathe it all straight back in again through your nose. Works especially well if you've had garlic. About twenty cloves.
You can't smell your own breath unless you do one of the above suggestions because smell is a sense which habituates - meaning you only notice a smell when its new to your nose. Once you get used to it, you cease to be able to smell it. That's why you can't smell your own breath and also why you stop noticing the smell of a nice or nasty odour after a while!
To be really sure, use an unscented part of your body - your inner forearm is ideal. Stretch your tongue out as far as you can, and lick along your arm for about six inches. Allow the saliva to dry, and sniff. What ever odour you get - ideally none, is what your breath smells like at that moment.