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 $107.28   11.107%   $119.1956   $119.20   $119.20   $119.20  
  Purchase #2 $133.58   4.302%   $139.3266   $139.33   $139.35   $139.30  
  Purchase #3 $223.91   4.675%   $234.3778   $234.38   $234.40   $234.40  
  Purchase #4 $151.93   4.318%   $158.4903   $158.49   $158.50   $158.50  
  Purchase #5 $199.71   4.756%   $209.2082   $209.21   $209.20   $209.20  
  Purchase #6 $76.40   7.662%   $82.2538   $82.25   $82.25   $82.30  
  Purchase #7 $59.88   8.224%   $64.8045   $64.80   $64.80   $64.80  
  7 purchase totals = $952.69       $1,007.6568   $1,007.66   $1,007.70   $1,007.70