The Immediate Destination field is the bank's ABA Transit Routing number. This field is used for EFT (Electronic Funds Transfer). It is an eight digit number that Raiser's Edge uses when a transmission file is created for direct debit transactions.
The last number of the Transit/Routing Number is a check digit that The Raiser's Edge will calculate and put in the transmission file when it is created. Therefore, you only need to enter the first 8 digits of the Transit/Routing Number that the bank gave (the bank will give a 9-digit number).
To add an Immediate Destination number, navigate to Config > General in the Raiser's Edge. The field will be on the right side of the window about three fields down. Here is where you will enter the first 8 digits of your bank's Transit/Routing number.