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 $198.92   13.867%   $226.5042   $226.50   $226.50   $226.50  
  Purchase #2 $53.80   13.305%   $60.9581   $60.96   $60.95   $61.00  
  Purchase #3 $146.83   10.419%   $162.1282   $162.13   $162.15   $162.10  
  Purchase #4 $33.81   4.828%   $35.4423   $35.44   $35.45   $35.40  
  Purchase #5 $65.29   7.247%   $70.0216   $70.02   $70.00   $70.00  
  Purchase #6 $208.34   7.759%   $224.5051   $224.51   $224.50   $224.50  
  Purchase #7 $22.73   8.748%   $24.7184   $24.72   $24.70   $24.70  
  7 purchase totals = $729.72       $804.2779   $804.28   $804.25   $804.20