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 $61.41   11.479%   $68.4593   $68.46   $68.45   $68.50  
  Purchase #2 $176.27   10.218%   $194.2813   $194.28   $194.30   $194.30  
  Purchase #3 $59.87   10.772%   $66.3192   $66.32   $66.30   $66.30  
  Purchase #4 $56.28   8.194%   $60.8916   $60.89   $60.90   $60.90  
  Purchase #5 $244.88   9.847%   $268.9933   $268.99   $269.00   $269.00  
  Purchase #6 $42.27   12.154%   $47.4075   $47.41   $47.40   $47.40  
  Purchase #7 $169.86   9.596%   $186.1598   $186.16   $186.15   $186.20  
  7 purchase totals = $810.84       $892.5120   $892.51   $892.50   $892.60