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 $88.54   8.391%   $95.9694   $95.97   $95.95   $96.00  
  Purchase #2 $33.93   5.190%   $35.691   $35.69   $35.70   $35.70  
  Purchase #3 $29.42   12.465%   $33.0872   $33.09   $33.10   $33.10  
  Purchase #4 $101.86   7.489%   $109.4883   $109.49   $109.50   $109.50  
  Purchase #5 $189.57   12.863%   $213.9544   $213.95   $213.95   $214.00  
  Purchase #6 $20.96   13.339%   $23.7559   $23.76   $23.75   $23.80  
  Purchase #7 $26.73   13.857%   $30.434   $30.43   $30.45   $30.40  
  7 purchase totals = $491.01       $542.3802   $542.38   $542.40   $542.50