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 $108.58   5.600%   $114.6605   $114.66   $114.65   $114.70  
  Purchase #2 $13.57   8.305%   $14.697   $14.70   $14.70   $14.70  
  Purchase #3 $184.38   11.189%   $205.0103   $205.01   $205.00   $205.00  
  Purchase #4 $84.83   8.639%   $92.1585   $92.16   $92.15   $92.20  
  Purchase #5 $182.92   12.782%   $206.3008   $206.30   $206.30   $206.30  
  Purchase #6 $30.45   6.111%   $32.3108   $32.31   $32.30   $32.30  
  Purchase #7 $12.63   3.145%   $13.0272   $13.03   $13.05   $13.00  
  7 purchase totals = $617.36       $678.1651   $678.17   $678.15   $678.20