just return the array, no need to assign it to anything. i.e.
return array('cashierId'=>$BillsCashierID ,
                      'CashierTotal'=>$CashierTotal ,
                      'CashierLastTotal'=>$CashierLastTotal ); 
or do
$cashier_data = array('cashierId'=>$BillsCashierID ,
                      'CashierTotal'=>$CashierTotal ,
                      'CashierLastTotal'=>$CashierLastTotal ); 
return $cashier_data;
then when you return it with $cd = GetCashierDetail(1); you can access $cd['CashierTotal']