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 $24.38   3.601%   $25.2579   $25.26   $25.25   $25.30  
  Purchase #2 $165.62   11.372%   $184.4543   $184.45   $184.45   $184.50  
  Purchase #3 $114.33   12.305%   $128.3983   $128.40   $128.40   $128.40  
  Purchase #4 $158.38   7.601%   $170.4185   $170.42   $170.40   $170.40  
  Purchase #5 $84.43   11.593%   $94.218   $94.22   $94.20   $94.20  
  Purchase #6 $118.41   12.265%   $132.933   $132.93   $132.95   $132.90  
  Purchase #7 $154.26   10.364%   $170.2475   $170.25   $170.25   $170.20  
  7 purchase totals = $819.81       $905.9275   $905.93   $905.90   $905.90