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 $158.53   6.133%   $168.2526   $168.25   $168.25   $168.30  
  Purchase #2 $139.95   4.161%   $145.7733   $145.77   $145.75   $145.80  
  Purchase #3 $126.84   4.532%   $132.5884   $132.59   $132.60   $132.60  
  Purchase #4 $191.67   4.600%   $200.4868   $200.49   $200.50   $200.50  
  Purchase #5 $232.36   9.826%   $255.1917   $255.19   $255.20   $255.20  
  Purchase #6 $244.57   6.812%   $261.2301   $261.23   $261.25   $261.20  
  Purchase #7 $247.51   8.163%   $267.7142   $267.71   $267.70   $267.70  
  7 purchase totals = $1,341.43       $1,431.2371   $1,431.23   $1,431.25   $1,431.30