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 $208.74   8.850%   $227.2135   $227.21   $227.20   $227.20  
  Purchase #2 $167.57   6.256%   $178.0532   $178.05   $178.05   $178.10  
  Purchase #3 $136.67   11.757%   $152.7383   $152.74   $152.75   $152.70  
  Purchase #4 $50.51   3.530%   $52.293   $52.29   $52.30   $52.30  
  Purchase #5 $233.93   9.574%   $256.3265   $256.33   $256.35   $256.30  
  Purchase #6 $239.97   6.549%   $255.6856   $255.69   $255.70   $255.70  
  Purchase #7 $10.67   5.137%   $11.2181   $11.22   $11.20   $11.20  
  7 purchase totals = $1,048.06       $1,133.5282   $1,133.53   $1,133.55   $1,133.50