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 $237.30   13.414%   $269.1314   $269.13   $269.15   $269.10  
  Purchase #2 $190.85   13.131%   $215.9105   $215.91   $215.90   $215.90  
  Purchase #3 $11.99   13.553%   $13.615   $13.62   $13.60   $13.60  
  Purchase #4 $160.46   9.793%   $176.1738   $176.17   $176.15   $176.20  
  Purchase #5 $113.66   8.384%   $123.1893   $123.19   $123.20   $123.20  
  Purchase #6 $183.25   9.509%   $200.6752   $200.68   $200.70   $200.70  
  Purchase #7 $148.73   8.738%   $161.726   $161.73   $161.75   $161.70  
  7 purchase totals = $1,046.24       $1,160.4212   $1,160.43   $1,160.45   $1,160.40