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 $67.72   8.688%   $73.6035   $73.60   $73.60   $73.60  
  Purchase #2 $151.91   9.523%   $166.3764   $166.38   $166.40   $166.40  
  Purchase #3 $98.80   13.640%   $112.2763   $112.28   $112.30   $112.30  
  Purchase #4 $242.70   11.828%   $271.4066   $271.41   $271.40   $271.40  
  Purchase #5 $32.41   10.466%   $35.802   $35.80   $35.80   $35.80  
  Purchase #6 $130.98   6.305%   $139.2383   $139.24   $139.25   $139.20  
  Purchase #7 $178.28   5.870%   $188.745   $188.75   $188.75   $188.70  
  7 purchase totals = $902.80       $987.4481   $987.46   $987.50   $987.40