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 $173.76   6.845%   $185.6539   $185.65   $185.65   $185.70  
  Purchase #2 $106.79   7.394%   $114.6861   $114.69   $114.70   $114.70  
  Purchase #3 $117.65   4.340%   $122.756   $122.76   $122.75   $122.80  
  Purchase #4 $185.76   4.230%   $193.6176   $193.62   $193.60   $193.60  
  Purchase #5 $40.71   8.183%   $44.0413   $44.04   $44.05   $44.00  
  Purchase #6 $237.48   10.324%   $261.9974   $262.00   $262.00   $262.00  
  Purchase #7 $96.30   4.720%   $100.8454   $100.85   $100.85   $100.80  
  7 purchase totals = $958.45       $1,023.5977   $1,023.61   $1,023.60   $1,023.60