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 $60.77   12.400%   $68.3055   $68.31   $68.30   $68.30  
  Purchase #2 $31.86   12.138%   $35.7272   $35.73   $35.75   $35.70  
  Purchase #3 $140.71   5.644%   $148.6517   $148.65   $148.65   $148.70  
  Purchase #4 $178.49   9.538%   $195.5144   $195.51   $195.50   $195.50  
  Purchase #5 $45.93   12.635%   $51.7333   $51.73   $51.75   $51.70  
  Purchase #6 $57.93   8.325%   $62.7527   $62.75   $62.75   $62.80  
  Purchase #7 $242.66   5.302%   $255.5258   $255.53   $255.55   $255.50  
  7 purchase totals = $758.35       $818.2106   $818.21   $818.25   $818.20