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 $239.86   5.854%   $253.9014   $253.90   $253.90   $253.90  
  Purchase #2 $168.43   8.218%   $182.2716   $182.27   $182.25   $182.30  
  Purchase #3 $76.80   12.526%   $86.42   $86.42   $86.40   $86.40  
  Purchase #4 $10.95   6.221%   $11.6312   $11.63   $11.65   $11.60  
  Purchase #5 $163.25   9.345%   $178.5057   $178.51   $178.50   $178.50  
  Purchase #6 $46.67   13.585%   $53.0101   $53.01   $53.00   $53.00  
  Purchase #7 $206.38   10.337%   $227.7135   $227.71   $227.70   $227.70  
  7 purchase totals = $912.34       $993.4535   $993.45   $993.40   $993.40