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 $239.73   12.548%   $269.8113   $269.81   $269.80   $269.80  
  Purchase #2 $114.89   10.688%   $127.1694   $127.17   $127.15   $127.20  
  Purchase #3 $168.66   4.586%   $176.3947   $176.39   $176.40   $176.40  
  Purchase #4 $248.27   8.227%   $268.6952   $268.70   $268.70   $268.70  
  Purchase #5 $6.75   12.832%   $7.6162   $7.62   $7.60   $7.60  
  Purchase #6 $158.25   7.569%   $170.2279   $170.23   $170.25   $170.20  
  Purchase #7 $164.97   12.874%   $186.2082   $186.21   $186.20   $186.20  
  7 purchase totals = $1,101.52       $1,206.1229   $1,206.13   $1,206.10   $1,206.10