How do you get change using bitcoin?

I've been wondering...
Let's say I have a bitcoin, let's say it's worth $10,000.
And let's say I'm in Myer, an Australian company that accepts bit coin as payment
And I wanna buy a $100 shirt, but pay using bit coin
What do I get for my change?
Is the bit coin broken up into some kind of bit cents?
Thanks in advance
John