while (my $row = $csv->getline($FH))
{
  my %currentRow;
  @currentRow{@keys} = @$row;
  print "Current row: ", Dumper \%currentRow;
  my $uniqueKey = "$currentRow{Amount} & $currentRow{AmountId} & $currentRow{MRP}"; # Bad idea if '&' is allowed in either of those values
  push @{ $result{$uniqueKey} }, \%currentRow; # add the current row to the existing ones
}

print "Result: ", Dumper \%result;