NOrmally i would say don't tap to that, but last year a kid at my academy got his sternum broken from knee on belly, he had to get surgery, have it re broken because it didn't heal correctly....
That being said, if you're a coward and you're afraid of a little broken sternum then tap, if you're a man, like me......no jk i've tapped to it like 10 times from my instructor lol