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 $164.44   13.138%   $186.0441   $186.04   $186.05   $186.00  
  Purchase #2 $69.74   6.765%   $74.4579   $74.46   $74.45   $74.50  
  Purchase #3 $11.35   3.370%   $11.7325   $11.73   $11.75   $11.70  
  Purchase #4 $217.61   4.388%   $227.1587   $227.16   $227.15   $227.20  
  Purchase #5 $216.97   10.605%   $239.9797   $239.98   $240.00   $240.00  
  Purchase #6 $142.38   12.218%   $159.776   $159.78   $159.80   $159.80  
  Purchase #7 $115.58   6.214%   $122.7621   $122.76   $122.75   $122.80  
  7 purchase totals = $938.07       $1,021.9110   $1,021.91   $1,021.95   $1,022.00