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 $9.29   8.296%   $10.0607   $10.06   $10.05   $10.10  
  Purchase #2 $116.61   8.870%   $126.9533   $126.95   $126.95   $127.00  
  Purchase #3 $105.63   6.181%   $112.159   $112.16   $112.15   $112.20  
  Purchase #4 $190.63   8.601%   $207.0261   $207.03   $207.05   $207.00  
  Purchase #5 $42.36   10.338%   $46.7392   $46.74   $46.75   $46.70  
  Purchase #6 $238.73   9.768%   $262.0491   $262.05   $262.05   $262.00  
  Purchase #7 $185.28   7.219%   $198.6554   $198.66   $198.65   $198.70  
  7 purchase totals = $888.53       $963.6428   $963.65   $963.65   $963.70