If you spray and wait a week or two for the vegatation to die off before rototilling, the tiller is just going to bring new weed seed to the germination zone. If you don't spray and go ahead and rototill today, the tiller is going to bring new weed seed to the germination zone.

So what I'd do is rototill first, wait a few weeks for the weeds to germinate, then spray (or till a 2nd time, about 1" deep) and plant. Spraying and then tilling is a waste of time and money in my book.