Two startup fails and two rolling retest fails would be judged completely different.
It depends how much time in between fails you allow. If it was due to contamination then yes defintiely blow again, start up and drive for a couple more retests to prove it was a false positive. BUT, if you cannot stop yourself from drinking responsibly and blow a fail then best to leave it alone. You may get a letter asking what happened but if you have a good record of no fails then the chance of an extension is low. I would advise you to learn your BAC math. While not completely dead on, it is good for general use.