for my $hashRef ( @$my_array_ref ) # Curlies aren't needed here since $my_array_ref is a simple variable name
{
  ...
}


##</code><code>##

$results->{$transactionType}{$purchasedThing} += $amountSpent

##</code><code>##

for my $transactionType (sort keys %$results)
{
  for my $purchasedThings (sort keys %{ $results->{$transactionType} }) # Curlies here to mark out what to dereference
  {
    printf("spent \$%5d on %20s using %20s\n",
      $results->{$transactionType}{$purchasedThings},
      $purchasedThings,
      $transactionType,
      );
  }
}