Try like this,
string lst = "";
foreach (ListItem lists in Your_DynamicCheckBoxID.Items)
{
lst = lists.ToString() + "," + lst;
string StringAdd= lst.ToString();
int comma = StringAdd.LastIndexOf(',');
string FinalString= StringAdd.Substring(0, comma);
}
This FinalString Returns all selected text from your dynamic check box list.You can store this string value to your Table (T_Transaction) by using insert query.
If you want to store each selected value seperately,just omit StringAdd, FinalString and just pass string lst value to your database.