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 $51.63   5.847%   $54.6488   $54.65   $54.65   $54.60  
  Purchase #2 $249.87   9.388%   $273.3278   $273.33   $273.35   $273.30  
  Purchase #3 $234.31   11.451%   $261.1408   $261.14   $261.15   $261.10  
  Purchase #4 $13.58   9.777%   $14.9077   $14.91   $14.90   $14.90  
  Purchase #5 $61.83   4.764%   $64.7756   $64.78   $64.80   $64.80  
  Purchase #6 $122.76   8.864%   $133.6414   $133.64   $133.65   $133.60  
  Purchase #7 $60.45   11.587%   $67.4543   $67.45   $67.45   $67.50  
  7 purchase totals = $794.43       $869.8964   $869.90   $869.95   $869.80