It depends on how you define things on if it has a lower bound. If you're talking percentage, it's infinite. It's Zeno's Paradox. If you decrease by half, then decrease it again the second halving is less than the first, and this continues forever, never reaching zero. It approaches zero as we take the limit to infinity, but we can never reach infinity obviously, and yes, we could divide a penny if we need to. Since inflation and deflation work on percentages, not descrete values, deflation could never reach zero.

Inflation is a useful tool though. It makes it so spending money now is better than saving. Deflation makes saving money better, which slows the economy. Basically, things have to go very wrong to make deflation happen because tools will be used to prevent that.