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 $63.82   8.463%   $69.2211   $69.22   $69.20   $69.20  
  Purchase #2 $198.62   5.203%   $208.9542   $208.95   $208.95   $209.00  
  Purchase #3 $102.35   11.873%   $114.502   $114.50   $114.50   $114.50  
  Purchase #4 $165.93   12.237%   $186.2349   $186.23   $186.25   $186.20  
  Purchase #5 $221.63   9.305%   $242.2527   $242.25   $242.25   $242.30  
  Purchase #6 $117.68   3.230%   $121.4811   $121.48   $121.50   $121.50  
  Purchase #7 $250.47   8.402%   $271.5145   $271.51   $271.50   $271.50  
  7 purchase totals = $1,120.50       $1,214.1605   $1,214.14   $1,214.15   $1,214.20