I trade my IRA in a Schwab account and they seem to be pretty lax on these rules. On occasion an OB has even put me in a negative cash position which I corrected with a sale as soon as I noticed. I'm sure I'd get a cash call if I tried to carry negative cash overnight though.
What about the new daytrading rules effective since last September? According to SEC for cash accounts (all IRAs are cash accounts) you cannot make more than 4 daytrades in any 5 concecutive days. If you do, your account will be closed.