15/100 is a periodic number in binary, so it can't be stored accurately as a float.

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1.15 base10 = 1.001001 base2
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This error causes 3010*1.15 to be equal to 3461.4999999999995, which Math::Round is correctly rounding to 3461.

You need to incorporate a tolerance. Since 1/2 can be stored precisely in a floating point number (0.5₁₀ = 0.1₂), you can use the following:

use feature qw( say );
use Math::Round qw( round );

my $x = 3010*1.15;
say round($x);
say round(round($x * 10**5) / 10**5);  # 5 decimal places of precision
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3461
3462
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This is basically what tye did by stringifying the number, except he let Perl "choose" the factor.