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 $241.86   8.198%   $261.6877   $261.69   $261.70   $261.70  
  Purchase #2 $245.91   9.776%   $269.9502   $269.95   $269.95   $270.00  
  Purchase #3 $112.89   7.411%   $121.2563   $121.26   $121.25   $121.30  
  Purchase #4 $92.69   4.203%   $96.5858   $96.59   $96.60   $96.60  
  Purchase #5 $190.74   4.715%   $199.7334   $199.73   $199.75   $199.70  
  Purchase #6 $248.61   6.794%   $265.5006   $265.50   $265.50   $265.50  
  Purchase #7 $200.52   10.826%   $222.2283   $222.23   $222.25   $222.20  
  7 purchase totals = $1,333.22       $1,436.9423   $1,436.95   $1,437.00   $1,437.00