Well, in this one the right way to answer it is to search a little bit about how the Roman society worked, and how its economy worked as a whole.
With that said, we already know that the Roman empire was agrarian, that means that most of the times they were exchanging food products, such as wine for example. But they used a coin to trade these commodities, called Solidus, assembled during Constantine II era. With that on point, we need to make a comparison between the Roman empire (its economy), trade markets and etc, with the shopping malls of today, as it's asked on the question. For that, I select the Forum of Trajan, a place that people used to buy and sell products.