When converting a monetary amount that includes a fractional amount of the lowest possible denomination into the closest real amount, use the "round to even" method of rounding to avoid trending upward. See Rounding#Round-to-even_method for specifics on this method of rounding, implemented in Math::BigFloat->ffround. Examples: 
1.5000 -> $1.50
1.5050 -> $1.50
1.5051 -> $1.51

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and 
1.5100 -> $1.51
1.5150 -> $1.52

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Edit: Adding a list of relevant links that may be of interest. 

sub monetize {
 require Math::BigFloat;
 #Defaults to a real $USD amount, rounding to nearest penny
 Math::BigFloat->new($_[0])->ffround( $_[1] || -2 );
}

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In reply to Proper monetary rounding by blogical

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