Santa Rosa de Lima is well known for having many stores, but be warned the stores are not like a store you would find in a developed country but more like home-stores. Home-store are peoples homes turned into a store this happened after the opening of borders with Honduras which led to many Hondurans entering the country to buy Salvadorean products which led to many families opening stores all over the place.
technology
Once you are in the city you if you are looking for any technological stuff you won't find much in the city, but there are some stores that sell technological stuff.
clothing
In the city you will notice that they sell many familiar clothing you would find in the USA but for more lower prices. For example, a Lacoste shirt will usually cost 40 to 50 dollars, there you will find the same shirt for 5 dollars. If you are going to purchase clothing take cash with you not a credit or debit card since there aren't any card machines.