round to two decimals

I'm doing a query in laravel to bring me a sum according to the field I'm calling, my problem is that I make a conversion to get the average and I need to round to two decimals, and use the function round for me to round to two decimals but I'm not rounding it, maybe I'm implementing it badly or I do not know how it works, I'll leave the laravel code to collaborate with me

$collection = Precebo::join('granjas','granjas.id','=','formulario_precebo.granja_id')
            ->select('granja_id','granjas.nombre_granja','año_destete',DB::raw('sum(numero_inicial) as total'))
            ->whereIn('año_destete',$request->desde)
            ->groupBy('granjas.nombre_granja','año_destete')->get(); 

            $arrayT = [];
            foreach ($collection as $value) {
                $arrayT[]=[$value->granja_id,$value->nombre_granja,$value->total,$value->año_destete];
            }

            $granjas = $request->array;
            $annios = $request->desde;

            $an = $request->annos;

            $categories = array();

            foreach ($annios as $years) {
                foreach ($an as $y) {
                    if ($years == $y) {
                        $categories[] = $y;
                    }
                }
            }

            $array = array();
            $promedios = array();

            foreach ($granjas as $granja) {
                $values = array();
                foreach ($annios as $year) {
                    $anoencontrado = 0;
                    foreach ($arrayT as $data) {
                        if ($granja == $data[0]) {
                            $value = $data[3] ? $data[2] : 0;
                            if ($data[3] == $year) {
                                $values[] = $value;
                                $anoencontrado = 1;
                            }
                        }
                    }
                    if ($anoencontrado === 0) {
                        $values[] = 0;
                    }
                }
                foreach ($arrayT as $data) {
                    if ($granja == $data[0]) {
                        $array[]=array(
                            'name' => $data[1],
                            'data' => $values
                        );
                        $suma = 0;
                        foreach ($values as $value) {
                            $suma += $value;
                        }
                        $promedios[]= array(
                            'name'=> $data[1],
                            'value'=>(count($values) !== 0)? $suma / count($values) : 0
                        );
                        break;
                    }
                }
            }
            $suma = 0;
            $suma_granjas = 0;
            foreach ($array as $arra) {
                $suma_granjas++;
            }
            foreach ($promedios as $promedio) {
                $suma += $promedio['value'];
            }
            $promedioGeneral = ($suma_granjas !== 0) ? $suma / $suma_granjas : 0;
            round($promedioGeneral);

            return response()->json(['status'=>'success','data'=>$array,'categories'=>$categories,'general'=>$promedioGeneral,'granjas'=>$suma_granjas],200);