use Sub::ScopeFinalizer qw( scope_finalizer );

{
   my $in_trans = eval { $dbh->begin_work() };
   my $pending_rollback = scope_finalizer {
      local $@;
      eval { $dbh->rollback() } if $in_trans;
   };

   code_that_touches_db();

   $pending_rollback->disable();
   $dbh->commit() if $in_trans;
}