I might get you wrong but is it correct that you have a list(table) of stores and the sales in another table?
For QlikView to relate the 2 tables the tables need to have a common field name, e.g. StoreId, If you have this the connection between selecting a store in the store list will automatically give you the sales for that store and selecting a sale will also show you from which store it sources.
A crosstable load may be the easy way to map your data from its current layout to one that will allow QlikView to easily do what you're talking about. Basically, it converts all of your field names (the stores) to field values. So it's going in the opposite direction of what you're asking for, but I believe accomplishes the same thing overall.
Assuming I didn't make a mistake, this:
CROSSTABLE LOAD (Store, Sales)
LOAD * INLINE [
Store1, Store2, Store3, Store4
500, 600, 700, 800
Should give you this table: