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 $238.94   9.243%   $261.0252   $261.03   $261.05   $261.00  
  Purchase #2 $49.92   3.202%   $51.5184   $51.52   $51.50   $51.50  
  Purchase #3 $246.54   6.315%   $262.109   $262.11   $262.10   $262.10  
  Purchase #4 $91.41   11.318%   $101.7558   $101.76   $101.75   $101.80  
  Purchase #5 $226.45   9.704%   $248.4247   $248.42   $248.40   $248.40  
  Purchase #6 $11.35   5.609%   $11.9866   $11.99   $12.00   $12.00  
  Purchase #7 $60.61   8.773%   $65.9273   $65.93   $65.95   $65.90  
  7 purchase totals = $925.22       $1,002.7470   $1,002.76   $1,002.75   $1,002.70