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 $182.63   11.730%   $204.0525   $204.05   $204.05   $204.10  
  Purchase #2 $143.88   6.136%   $152.7085   $152.71   $152.70   $152.70  
  Purchase #3 $57.46   3.148%   $59.2688   $59.27   $59.25   $59.30  
  Purchase #4 $158.43   7.135%   $169.734   $169.73   $169.75   $169.70  
  Purchase #5 $117.51   10.748%   $130.14   $130.14   $130.15   $130.10  
  Purchase #6 $217.58   11.535%   $242.6779   $242.68   $242.70   $242.70  
  Purchase #7 $35.26   8.339%   $38.2003   $38.20   $38.20   $38.20  
  7 purchase totals = $912.75       $996.7820   $996.78   $996.80   $996.80