var regi = (from r in db.Registrs.ToList()
                            group r by new
                            {
                                Date = checkBox1.Checked ? (DateTime?)r.date : (DateTime?)null,
                                Company = checkBox2.Checked ? r.company : null,
                                City = checkBox3.Checked ? r.city : null,
                                Country = checkBox4.Checked ? r.country : null,
                                Manager = checkBox5.Checked ? r.manager : null,
                            } into g
                            select new
                            {
                                Date = checkBox1.Checked ? (DateTime?)g.Key.Date : (DateTime?)null,
                                Company = checkBox2.Checked ? g.Key.Company : null,
                                City = checkBox3.Checked ? g.Key.City : null,
                                Country = checkBox4.Checked ? g.Key.Country : null,
                                Manager = checkBox5.Checked ? g.Key.Manager : null,
                                Quantity = checkBox1.Checked || checkBox2.Checked || checkBox3.Checked || checkBox4.Checked || checkBox5.Checked ? g.Sum(s => s.quantity) : null,
                                Amount = checkBox1.Checked || checkBox2.Checked || checkBox3.Checked || checkBox4.Checked || checkBox5.Checked ? g.Sum(s => s.amount) : null,
                            }).Distinct();

                registrDataGridView.DataSource = regi.ToList();