Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.76   6.454%   $255.2341   $255.23   $255.25   $255.20  
  Purchase #2 $249.98   4.407%   $260.9966   $261.00   $261.00   $261.00  
  Purchase #3 $230.32   5.290%   $242.5039   $242.50   $242.50   $242.50  
  Purchase #4 $231.60   12.785%   $261.2101   $261.21   $261.20   $261.20  
  Purchase #5 $54.66   8.823%   $59.4827   $59.48   $59.50   $59.50  
  Purchase #6 $35.41   4.273%   $36.9231   $36.92   $36.90   $36.90  
  Purchase #7 $243.65   4.527%   $254.68   $254.68   $254.70   $254.70  
  7 purchase totals = $1,285.38       $1,371.0305   $1,371.02   $1,371.05   $1,371.00