Postgresql – Begin Transaction Rollback

I just wanted to know what would happen if there are multiple insert and update statements like (insert into sales(),insert into saledetails(), update sale etc.) getting executed and if any exception occurs then will be a rollback of all or the line in which the exception occurs. Below is the code.

using (var conn = new NpgsqlConnection(connstr))
                        {
                            conn.Open();
                            var tra = conn.BeginTransaction();
                            try
                            {
                                NpgsqlCommand cmd = new NpgsqlCommand();
                                cmd.Connection = conn;
                                cmd.CommandType = CommandType.Text;
                                cmd.CommandTimeout = 0;
                                cmd.CommandText = strQueryBuild.ToString();
                                RowsAffected = cmd.ExecuteNonQuery();
                                tra.Commit();
                                commitstatus = true;
                            }
                            catch (Exception ex)
                            {
                                commitstatus = false;
                                AppHelper.ErrrorLog(ex, "UploadFileData-Error1");
                                RowsAffected = -1;
                                tra.Rollback();
                            }
                            
                        }

I am getting a duplicate key violation error after executing again that query.