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 $190.76   8.166%   $206.3375   $206.34   $206.35   $206.30  
  Purchase #2 $101.37   3.499%   $104.9169   $104.92   $104.90   $104.90  
  Purchase #3 $119.33   4.129%   $124.2571   $124.26   $124.25   $124.30  
  Purchase #4 $70.34   4.302%   $73.366   $73.37   $73.35   $73.40  
  Purchase #5 $250.26   11.461%   $278.9423   $278.94   $278.95   $278.90  
  Purchase #6 $44.44   9.836%   $48.8111   $48.81   $48.80   $48.80  
  Purchase #7 $56.81   4.138%   $59.1608   $59.16   $59.15   $59.20  
  7 purchase totals = $833.31       $895.7917   $895.80   $895.75   $895.80