Minimum billable time unit - industry standard for contract programming?

Question

We're a client that recently hired a contract programming company for some fairly focused work (essentially writing 'scripts' to extend the functionality of a third-party enterprise application). We're trying to evaluate their performance on and the value of some work they did for us, but we're a little new to using contract programmers and could use some help:

1. If you were hiring a company as a contractor to do computer program development for you, and the minimum billing time unit was not mentioned in the contract, would you expect to be billed in whole-hour increments (so that a phone call of 5 minutes is billed as 1 hour)?

2. What is industry standard practice for the minimum billable time unit in contract programming work?

3. If you hired a contracting company that had two employees, would you expect each person's time to be broken out and rounded up to the minimum billable time unit? Let's say the senior guy worked with the junior guy for 15 minutes, and the junior guy worked 4:15 that day. Would you take exception to a bill for 1 hour (senior guy) plus 5 hours (junior guy), or would you expect a bill for just 5 hours?

You may find my follow-up question about key contract points interesting.