I do know, and I did tell you to rethink your design.
If you had used Oracle it would have been much worse, Oracle cache the sequences, so if you restart the server you can get a gap of twenty numbers. and if you have a cluster server they won't even be in order.
(<for the nitpicks> I know it's a setting, but if you want higher performance you don't change it</for the nitpicks>)
People say nothing is impossible, but I do nothing every day.
The new IDENTITY value is generated when a row insert is initiated and will update the table's current identity value even when the transaction is rolled back. In simple terms, it would behave as if no rollback happened.
While Shameel and Russel gave you answers it is not the solution, if you are relying on the identity filed to give you sequential information (or any information) your design is WRONG. An ID field has only 1 function, to identify the record.
Never underestimate the power of human stupidity