@eve is correct. DUI's do not normally restrict entry however multiple offences could be considered a Crime Involving Moral Turpitude. The decision is at the sole discretion of the Border Security Officer.
Also, remember (and this is important!) you do not require a waiver until you have been denied entry. Do not preemptively assume you need a waiver until you are denied entry and they tell you that you need one. If you have been crossing before your jail sentence, I would continue to do so as you always have until they deny entry.