Pls try the "format" property of clientRowGroup's calculate like this:

                "clientRowGroup" => [
                    "productLine" => [
                        'direction' => 'desc',
                        'calculate' => [
                            'totalSales' => ['sum', 'dollar_sales',
                                "format" => "function(value) {return value.toLocaleString();}",
                            ], 

You could replace the javascript function toLocaleString() with any custom number format function or javascript code that you like. Let us know if this works for you. Rgds,