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 $58.43   9.156%   $63.7799   $63.78   $63.80   $63.80  
  Purchase #2 $46.86   5.423%   $49.4012   $49.40   $49.40   $49.40  
  Purchase #3 $61.48   4.531%   $64.2657   $64.27   $64.25   $64.30  
  Purchase #4 $38.73   10.813%   $42.9179   $42.92   $42.90   $42.90  
  Purchase #5 $246.95   5.787%   $261.241   $261.24   $261.25   $261.20  
  Purchase #6 $75.29   12.869%   $84.9791   $84.98   $85.00   $85.00  
  Purchase #7 $188.56   5.329%   $198.6084   $198.61   $198.60   $198.60  
  7 purchase totals = $716.30       $765.1932   $765.20   $765.20   $765.20