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 $40.54   10.569%   $44.8247   $44.82   $44.80   $44.80  
  Purchase #2 $238.98   9.614%   $261.9555   $261.96   $261.95   $262.00  
  Purchase #3 $46.87   6.439%   $49.888   $49.89   $49.90   $49.90  
  Purchase #4 $48.92   5.437%   $51.5798   $51.58   $51.60   $51.60  
  Purchase #5 $150.50   8.474%   $163.2534   $163.25   $163.25   $163.30  
  Purchase #6 $69.58   13.275%   $78.8167   $78.82   $78.80   $78.80  
  Purchase #7 $237.48   13.399%   $269.2999   $269.30   $269.30   $269.30  
  7 purchase totals = $832.87       $919.6180   $919.62   $919.60   $919.70