You could post the xml to the server and then process with XML::Twig and assign different code block to the different elements. Something like this;

Client code

#!/usr/bin/perl
use strict;
use LWP::UserAgent;

my $ua = LWP::UserAgent->new;
my $server_endpoint = "http://localhost/test/process2.cgi";   

# set custom HTTP request header fields
my $req = HTTP::Request->new(POST => $server_endpoint);
$req->header('content-type' => 'application/json');
my $xml = do { local $/; <DATA> };
$req->content($xml);

my $resp = $ua->request($req);
if ($resp->is_success) {
    my $message = $resp->decoded_content;
    print "Received reply:\n$message\n";
}
else {
    print "HTTP POST error code: ", $resp->code, "\n";
    print "HTTP POST error message: ", $resp->message, "\n";
}

__DATA__
<?xml version="1.0"?>
<data>
<customer-data>
  <customer>
    <first_name>Frank</first_name>
    <last_name>Sanbeans</last_name>
    <dob>3/10</dob>
    <email>frank@example.com</email>
  </customer>
  <customer>
    <first_name>Sandy</first_name>
    <last_name>Sanbeans</last_name>
    <dob>4/15</dob>
    <email>sandy@example.com</email>
  </customer>
</customer-data>
<supplier-data>
  <supplier>
    <name>Supplier 1</name>
    <address>Address 1</address>
    <tel-no>012345</tel-no>
  </supplier>
</supplier-data>
</data>
[download]

#!perl
use strict;
use CGI;
use DBI;
#use CGI::Carp 'fatalsToBrowser';
use XML::Twig;

my $dbh = dbh(); # connect
# customer database
my $sql1 = 'INSERT INTO c_details (f_name,l_name,dob,email) 
           VALUES (?,?,?,?)';
my $sth1 = $dbh->prepare($sql1);

# supplier database
my $sql2 = 'INSERT INTO s_details (name,address,tel_no) 
           VALUES (?,?,?)';
my $sth2 = $dbh->prepare($sql2);

my $cgi = CGI->new;                  
print $cgi->header(-type => "application/json", -charset => "utf-8");
my $xml = $cgi->param("POSTDATA");

# process file
my $t = XML::Twig->new(
  twig_handlers => { 
    'customer' => \&customer,
    'supplier' => \&supplier, }
);

$t->parse($xml);

sub customer {
  my ($t,$elt) = @_;
  my @f=();
  $f[0] = $elt->field('first_name');
  $f[1] = $elt->field('last_name');
  $f[2] = $elt->field('dob');
  $f[3] = $elt->field('email');  
  $sth1->execute(@f) or die $DBI::errstr;
  print join "\t",$sql1,@f,"\n";
}

sub supplier {
  my ($t,$elt) = @_;
  my @f=();
  $f[0] = $elt->field('name');
  $f[1] = $elt->field('address');
  $f[2] = $elt->field('tel-no');
  $sth2->execute(@f) or die $DBI::errstr;
  print join "\t",$sql2,@f,"\n";
}
[download]