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 $77.60   11.156%   $86.2571   $86.26   $86.25   $86.30  
  Purchase #2 $173.63   9.858%   $190.7464   $190.75   $190.75   $190.70  
  Purchase #3 $102.66   9.538%   $112.4517   $112.45   $112.45   $112.50  
  Purchase #4 $139.53   10.593%   $154.3104   $154.31   $154.30   $154.30  
  Purchase #5 $177.48   3.692%   $184.0326   $184.03   $184.05   $184.00  
  Purchase #6 $49.39   8.772%   $53.7225   $53.72   $53.70   $53.70  
  Purchase #7 $238.88   5.497%   $252.0112   $252.01   $252.00   $252.00  
  7 purchase totals = $959.17       $1,033.5319   $1,033.53   $1,033.50   $1,033.50