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 $244.94   3.131%   $252.6091   $252.61   $252.60   $252.60  
  Purchase #2 $165.28   13.103%   $186.9366   $186.94   $186.95   $186.90  
  Purchase #3 $208.91   4.168%   $217.6174   $217.62   $217.60   $217.60  
  Purchase #4 $33.62   8.105%   $36.3449   $36.34   $36.35   $36.30  
  Purchase #5 $173.33   13.428%   $196.6048   $196.60   $196.60   $196.60  
  Purchase #6 $47.27   4.605%   $49.4468   $49.45   $49.45   $49.40  
  Purchase #7 $210.89   6.379%   $224.3427   $224.34   $224.35   $224.30  
  7 purchase totals = $1,084.24       $1,163.9023   $1,163.90   $1,163.90   $1,163.70