VSarkiss is correct. Although I would switch to DBI (with RaiseError set), here's an approach:

eval {
    $dbh->nsql( "begin transaction" );
    $dbh->nsql( <update query 1> );
    die "problem with query 1" if $status == 0;
    .
    .
    $dbh->nsql( <update qurey n> ); 
    die "problem with query n" if $status == 0;
};

if( $@ ) {
   $dbh->nsql( "rollback" );
} else {
   $dbh->nsql( "commit" );
}
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-derby