[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi, Pack=1)]
  public struct TransactionRecord {
    public int    OrderID;
    private byte  _zipCode1,
                  _zipCode2,
                  _zipCode3,
                  _zipCode4,
                  _zipCode5;
    public char[] ZipCode {
      get {
         return new char[] {
                  (char)_zipCode1,
                  (char)_zipCode2,
                  (char)_zipCode3,
                  (char)_zipCode4,
                  (char)_zipCode5
                  };
       }
    }
}

In use, the code just coerces chunks of a binary buffer to/from this struct by way of unsafe pointer operations. Thus the need to explicitly define the layout, charset, and word alignment rules.