SQL Query - If/Then/Else Logic?

I have 3 tables:Sales data - SaleID, Date, StoreID, CategoryID, Cost, Retail

Store names - StoreID, Name
Category names - CategoryID, Name

I have a dgv bound to my sales table, and 2 comboboxes, one each bound to the remaining tables, with display member set to the name, and value member to the ID.

An ID of -1 represents "All Stores" or "All Categories"
An ID > -1 represents a specific location or category

So, can I use some sort of If,Then,Else logic to do something like this:

SELECT (*) FROM Sales
WHERE (IF @StoreID > -1 THEN StoreID = @StoreID ELSE True)
AND (IF @CategoryID > -1 THEN CategoryID = @CategoryID ELSE True)
AND Date BETWEEN @Date1 AND @Date2

I've found some different examples of If/Then/Else and Select Case type logic for SQL using google, but they don't seem to fit my situation, and I'm not sure how to apply that to what I'm attempting here.