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 $61.40   8.309%   $66.5017   $66.50   $66.50   $66.50  
  Purchase #2 $232.95   10.188%   $256.6829   $256.68   $256.70   $256.70  
  Purchase #3 $133.87   9.593%   $146.7121   $146.71   $146.70   $146.70  
  Purchase #4 $35.25   9.530%   $38.6093   $38.61   $38.60   $38.60  
  Purchase #5 $153.99   9.701%   $168.9286   $168.93   $168.95   $168.90  
  Purchase #6 $192.78   4.364%   $201.1929   $201.19   $201.20   $201.20  
  Purchase #7 $87.66   7.652%   $94.3677   $94.37   $94.35   $94.40  
  7 purchase totals = $897.90       $972.9952   $972.99   $973.00   $973.00