I've rewritten your code into a form that I think makes at least some sense:

use strict;
use warnings;

my $amt = 4887.15;

print " Checking amnt before conversion $amt,\n";
        $amt= sprintf("%.2f",$amt);
        print " Checking amnt after rounding $amt,\n";
        $amt = $amt*100;
        print " Checking amnt after conversion $amt,\n";
        printf "Checking the EXACT value of amnt: %.17g\n", $amt;

amnt($amt);

sub amnt
{
my $amount=$_[0];
$amount=int($amount);
print  "$amount i m checking amount before padding,\n";
#my $padamnt = sprintf("%016.0f",$amount);---> currently commented to 
+check integer effect.
my $padamnt = sprintf("%016d",$amount);

print  "$padamnt i m checking amount after padding,\n";
 return $padamnt;
}
[download]

When I run that script, I get:

 Checking amnt before conversion 4887.15,
 Checking amnt after rounding 4887.15,
 Checking amnt after conversion 488715,
Checking the EXACT value of amnt: 488714.99999999994
488714 i m checking amount before padding,
0000000000488714 i m checking amount after padding,
[download]

Note that I've added a line of code that demonstrates that the EXACT value of $amt is NOT 488715.
Perl's print() function frequently fails to produce an accurate representation of floating point values - and that's what is happening here.

That output I'm seeing is as I expect.
Which is the line of output that you don't understand ?

You need to stay alert to this aspect of perl's print() function.
Neither python3 nor raku are afflicted with such a poorly designed implementation:

$ python3 -c "print(4887.15 * 100)"
488714.99999999994

$ raku -e "say 4887.15e0 * 100"
488714.99999999994
[download]

Cheers,
Rob