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 $101.37   13.116%   $114.6657   $114.67   $114.65   $114.70  
  Purchase #2 $29.99   8.495%   $32.5377   $32.54   $32.55   $32.50  
  Purchase #3 $68.71   6.165%   $72.946   $72.95   $72.95   $72.90  
  Purchase #4 $192.99   4.702%   $202.0644   $202.06   $202.05   $202.10  
  Purchase #5 $185.84   6.862%   $198.5923   $198.59   $198.60   $198.60  
  Purchase #6 $22.54   7.784%   $24.2945   $24.29   $24.30   $24.30  
  Purchase #7 $176.25   5.686%   $186.2716   $186.27   $186.25   $186.30  
  7 purchase totals = $777.69       $831.3722   $831.37   $831.35   $831.40