Proper use of Transactions...

Greetings,

If I write a transaction like this:

begin transaction;
.
.
.
commit transaction;

and an error occurs somewhere in the middle, do I have to issue a rollback
command or will PostgreSQL do that automatically on an error?  The problem
I think I am having is that if some command between the begin and commit
statements causes an error, my program terminates, so I do not have an
opportunity to issue a rollback.

All this is compounded because I am using PHP3 as an Apache module to
access PostgreSQL and I am receiving the following error in my Apache log:

NOTICE:  (transaction aborted): queries ignored until END

I'm not sure where to start looking for the problem.  Any insight would be
greatly appreciated.

Thank you,
Matthew