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 $112.87   11.223%   $125.5374   $125.54   $125.55   $125.50  
  Purchase #2 $240.99   11.723%   $269.2413   $269.24   $269.25   $269.20  
  Purchase #3 $104.57   9.360%   $114.3578   $114.36   $114.35   $114.40  
  Purchase #4 $93.95   13.243%   $106.3918   $106.39   $106.40   $106.40  
  Purchase #5 $157.77   10.344%   $174.0897   $174.09   $174.10   $174.10  
  Purchase #6 $101.67   12.503%   $114.3818   $114.38   $114.40   $114.40  
  Purchase #7 $62.81   3.422%   $64.9594   $64.96   $64.95   $65.00  
  7 purchase totals = $874.63       $968.9592   $968.96   $969.00   $969.00