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 $110.95   3.592%   $114.9353   $114.94   $114.95   $114.90  
  Purchase #2 $53.71   4.844%   $56.3117   $56.31   $56.30   $56.30  
  Purchase #3 $146.31   13.203%   $165.6273   $165.63   $165.65   $165.60  
  Purchase #4 $176.83   8.252%   $191.422   $191.42   $191.40   $191.40  
  Purchase #5 $107.28   6.450%   $114.1996   $114.20   $114.20   $114.20  
  Purchase #6 $9.28   3.674%   $9.6209   $9.62   $9.60   $9.60  
  Purchase #7 $245.72   5.241%   $258.5982   $258.60   $258.60   $258.60  
  7 purchase totals = $850.08       $910.7150   $910.72   $910.70   $910.60