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 $238.63   9.421%   $261.1113   $261.11   $261.10   $261.10  
  Purchase #2 $154.26   5.120%   $162.1581   $162.16   $162.15   $162.20  
  Purchase #3 $96.76   5.222%   $101.8128   $101.81   $101.80   $101.80  
  Purchase #4 $112.53   8.602%   $122.2098   $122.21   $122.20   $122.20  
  Purchase #5 $8.88   10.653%   $9.826   $9.83   $9.85   $9.80  
  Purchase #6 $173.29   13.628%   $196.906   $196.91   $196.90   $196.90  
  Purchase #7 $232.76   7.494%   $250.203   $250.20   $250.20   $250.20  
  7 purchase totals = $1,017.11       $1,104.2270   $1,104.23   $1,104.20   $1,104.20