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 $53.71   9.582%   $58.8565   $58.86   $58.85   $58.90  
  Purchase #2 $238.49   9.779%   $261.8119   $261.81   $261.80   $261.80  
  Purchase #3 $23.89   4.304%   $24.9182   $24.92   $24.90   $24.90  
  Purchase #4 $248.39   7.759%   $267.6626   $267.66   $267.65   $267.70  
  Purchase #5 $64.73   6.792%   $69.1265   $69.13   $69.15   $69.10  
  Purchase #6 $11.90   12.680%   $13.4089   $13.41   $13.40   $13.40  
  Purchase #7 $213.66   10.748%   $236.6242   $236.62   $236.60   $236.60  
  7 purchase totals = $854.77       $932.4088   $932.41   $932.35   $932.40