my $sql2 = qq/
     INSERT INTO transaction_details (quantity, gross_sales) 
      VALUES (?,  convert (money, ?))
     /;# using bind parameters
   my $sth = $dbh->prepare($sql);

# Assuming that each row in the form has the form
#  {fieldname}_{rownnum}
   my %param = $cgi->Vars();
   while my $key (grep /quantity_/ keys %param) {  
     my $quantity = $cgi->param($key);
     $key =~ m/(\d+)$/;
     my $gross_sales = $cgi->param("gross_sales_$1");
     my $rv = $sth->execute( $quantity, $gross_sales );
   }