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 $114.33   9.291%   $124.9524   $124.95   $124.95   $125.00  
  Purchase #2 $137.94   6.113%   $146.3723   $146.37   $146.35   $146.40  
  Purchase #3 $13.46   6.526%   $14.3384   $14.34   $14.35   $14.30  
  Purchase #4 $249.92   6.513%   $266.1973   $266.20   $266.20   $266.20  
  Purchase #5 $144.66   5.831%   $153.0951   $153.10   $153.10   $153.10  
  Purchase #6 $32.90   8.660%   $35.7491   $35.75   $35.75   $35.70  
  Purchase #7 $191.95   12.303%   $215.5656   $215.57   $215.55   $215.60  
  7 purchase totals = $885.16       $956.2702   $956.28   $956.25   $956.30