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 $12.87   5.853%   $13.6233   $13.62   $13.60   $13.60  
  Purchase #2 $61.56   11.463%   $68.6166   $68.62   $68.60   $68.60  
  Purchase #3 $182.77   8.206%   $197.7681   $197.77   $197.75   $197.80  
  Purchase #4 $159.30   3.258%   $164.49   $164.49   $164.50   $164.50  
  Purchase #5 $247.46   5.172%   $260.2586   $260.26   $260.25   $260.30  
  Purchase #6 $67.39   9.626%   $73.877   $73.88   $73.90   $73.90  
  Purchase #7 $126.99   4.137%   $132.2436   $132.24   $132.25   $132.20  
  7 purchase totals = $858.34       $910.8772   $910.88   $910.85   $910.90