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 $43.33   6.228%   $46.0286   $46.03   $46.05   $46.00  
  Purchase #2 $56.51   3.854%   $58.6879   $58.69   $58.70   $58.70  
  Purchase #3 $250.34   3.821%   $259.9055   $259.91   $259.90   $259.90  
  Purchase #4 $47.26   12.692%   $53.2582   $53.26   $53.25   $53.30  
  Purchase #5 $104.71   4.339%   $109.2534   $109.25   $109.25   $109.30  
  Purchase #6 $218.27   7.252%   $234.0989   $234.10   $234.10   $234.10  
  Purchase #7 $217.68   5.292%   $229.1996   $229.20   $229.20   $229.20  
  7 purchase totals = $938.10       $990.4321   $990.44   $990.45   $990.50