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 $206.41   12.612%   $232.4424   $232.44   $232.45   $232.40  
  Purchase #2 $59.89   8.321%   $64.8734   $64.87   $64.85   $64.90  
  Purchase #3 $50.76   12.793%   $57.2537   $57.25   $57.25   $57.30  
  Purchase #4 $115.54   9.228%   $126.202   $126.20   $126.20   $126.20  
  Purchase #5 $102.42   11.201%   $113.8921   $113.89   $113.90   $113.90  
  Purchase #6 $151.82   7.693%   $163.4995   $163.50   $163.50   $163.50  
  Purchase #7 $42.59   4.694%   $44.5892   $44.59   $44.60   $44.60  
  7 purchase totals = $729.43       $802.7523   $802.74   $802.75   $802.80