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 $62.72   4.256%   $65.3894   $65.39   $65.40   $65.40  
  Purchase #2 $25.43   10.806%   $28.178   $28.18   $28.20   $28.20  
  Purchase #3 $212.37   7.713%   $228.7501   $228.75   $228.75   $228.80  
  Purchase #4 $60.38   3.855%   $62.7076   $62.71   $62.70   $62.70  
  Purchase #5 $209.62   8.256%   $226.9262   $226.93   $226.95   $226.90  
  Purchase #6 $28.65   5.253%   $30.155   $30.16   $30.15   $30.20  
  Purchase #7 $247.44   5.506%   $261.064   $261.06   $261.05   $261.10  
  7 purchase totals = $846.61       $903.1703   $903.18   $903.20   $903.30