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 $65.36   3.514%   $67.6568   $67.66   $67.65   $67.70  
  Purchase #2 $241.78   11.477%   $269.5291   $269.53   $269.55   $269.50  
  Purchase #3 $128.99   3.683%   $133.7407   $133.74   $133.75   $133.70  
  Purchase #4 $235.43   5.510%   $248.4022   $248.40   $248.40   $248.40  
  Purchase #5 $59.28   8.655%   $64.4107   $64.41   $64.40   $64.40  
  Purchase #6 $48.81   9.531%   $53.4621   $53.46   $53.45   $53.50  
  Purchase #7 $132.63   8.155%   $143.446   $143.45   $143.45   $143.40  
  7 purchase totals = $912.28       $980.6476   $980.65   $980.65   $980.60