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 $95.81   3.141%   $98.8194   $98.82   $98.80   $98.80  
  Purchase #2 $95.25   4.258%   $99.3057   $99.31   $99.30   $99.30  
  Purchase #3 $45.62   8.653%   $49.5675   $49.57   $49.55   $49.60  
  Purchase #4 $33.50   5.859%   $35.4628   $35.46   $35.45   $35.50  
  Purchase #5 $114.41   13.223%   $129.5384   $129.54   $129.55   $129.50  
  Purchase #6 $153.33   6.437%   $163.1999   $163.20   $163.20   $163.20  
  Purchase #7 $203.67   3.563%   $210.9268   $210.93   $210.95   $210.90  
  7 purchase totals = $741.59       $786.8205   $786.83   $786.80   $786.80