Of course, with any food product - it depends on how you've treated the food after you've opened and processed it.

The advantage you have with marinara sauce is that it's acidic - due to the tomatoes. The acidity slows microbial growth.

But if it's been sitting outside for a while after you've opened it, it's had greater opportunity to gather various bacteria and fungal spores and generally being a nice warm pleasant temperature for spore like objects to get it on and subsequently make you sick as a dog when you eat the product of their unholy union.

However, if you put it in the fridge and your fridge is properly chilled, you can probably squeeze a week or two out of it. I've gotten about two weeks out of mine but I still do a sniff test after two weeks.

Pretty much the rule of thumb remails - when in doubt, throw it out. Better to waste a couple of bucks in food than to spend a night on or over a porcelain throne in misery.