Can ripple currency units be integers? I understand with Ripple that anyone on the network can offer their own currency.  Someone cited the example of airline frequent flier miles.

Airline miles, in my experience, come in whole numbers.  I.e. 2000 miles, not 1999.5 miles.

If I start trading miles on Ripple, someone could easily offer to buy or sell in fractional units.  So balances in ripple wallets could be 1999.5 miles, right?

Is there any way in Ripple to force the units of a particular currency to be integers?

I'm asking about what appears in the wallets.  I know that within the system the units are integers.  I.e. 1 XRP = 1,000,000 drops.  I'm asking about the balances shown to users in their wallets.
Gateways can refuse to issue or redeem fractional amounts and users can refuse to pay them. But there is no authority to say to someone "you may not hold a fractional amount of this currency". Nobody can stop you from holding fractional amounts if you wish to.