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 $62.81   7.108%   $67.2745   $67.27   $67.25   $67.30  
  Purchase #2 $83.55   10.785%   $92.5609   $92.56   $92.55   $92.60  
  Purchase #3 $28.59   12.586%   $32.1883   $32.19   $32.20   $32.20  
  Purchase #4 $161.85   8.735%   $175.9876   $175.99   $176.00   $176.00  
  Purchase #5 $130.49   8.616%   $141.733   $141.73   $141.75   $141.70  
  Purchase #6 $127.69   5.131%   $134.2418   $134.24   $134.25   $134.20  
  Purchase #7 $158.97   4.756%   $166.5306   $166.53   $166.55   $166.50  
  7 purchase totals = $753.95       $810.5167   $810.51   $810.55   $810.50