If I have had my record expunged, can I answer "no" to a question that asks me If I have ever had convictions? In theory, yes, but in practical terms, just because your conviction has been expunged at the courthouse does not mean that there aren't a number of other records of your arrest and conviction that exist and that are likely to be found if the employer does a criminal background check.
The safest answer is always the truthful answer.