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 $250.39   4.272%   $261.0867   $261.09   $261.10   $261.10  
  Purchase #2 $161.86   6.197%   $171.8905   $171.89   $171.90   $171.90  
  Purchase #3 $226.58   4.697%   $237.2225   $237.22   $237.20   $237.20  
  Purchase #4 $99.75   5.608%   $105.344   $105.34   $105.35   $105.30  
  Purchase #5 $133.27   10.637%   $147.4459   $147.45   $147.45   $147.40  
  Purchase #6 $25.48   10.326%   $28.1111   $28.11   $28.10   $28.10  
  Purchase #7 $15.51   4.351%   $16.1848   $16.18   $16.20   $16.20  
  7 purchase totals = $912.84       $967.2855   $967.28   $967.30   $967.20