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 $28.34   8.304%   $30.6934   $30.69   $30.70   $30.70  
  Purchase #2 $197.63   13.537%   $224.3832   $224.38   $224.40   $224.40  
  Purchase #3 $87.82   7.162%   $94.1097   $94.11   $94.10   $94.10  
  Purchase #4 $237.37   10.682%   $262.7259   $262.73   $262.75   $262.70  
  Purchase #5 $217.95   12.443%   $245.0695   $245.07   $245.05   $245.10  
  Purchase #6 $100.70   9.705%   $110.4729   $110.47   $110.45   $110.50  
  Purchase #7 $199.51   5.199%   $209.8825   $209.88   $209.90   $209.90  
  7 purchase totals = $1,069.32       $1,177.3371   $1,177.33   $1,177.35   $1,177.40