{
    package BlahBlah;
    use Tie::Scalar;
    @ISA = 'Tie::StdScalar';
    sub STORE { ${+shift} = sprintf '%0.2f', pop }
}

tie my $foo, 'BlahBlah'; 

$foo = 1;
print "$foo\n";  # 1.00

$foo = 1.005;
print "$foo\n";  # 1.00

$foo = 1.025;
print "$foo\n";  # 1.02

$foo = 0;
print "$foo\n";  # 0.00