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 $69.27   13.273%   $78.4642   $78.46   $78.45   $78.50  
  Purchase #2 $114.41   9.754%   $125.5696   $125.57   $125.55   $125.60  
  Purchase #3 $62.46   4.246%   $65.1121   $65.11   $65.10   $65.10  
  Purchase #4 $247.86   3.629%   $256.8548   $256.85   $256.85   $256.90  
  Purchase #5 $49.85   13.692%   $56.6755   $56.68   $56.70   $56.70  
  Purchase #6 $185.53   12.108%   $207.994   $207.99   $208.00   $208.00  
  Purchase #7 $36.59   11.189%   $40.6841   $40.68   $40.70   $40.70  
  7 purchase totals = $765.97       $831.3543   $831.34   $831.35   $831.50