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 $240.95   4.548%   $251.9084   $251.91   $251.90   $251.90  
  Purchase #2 $229.39   11.492%   $255.7515   $255.75   $255.75   $255.80  
  Purchase #3 $102.80   13.778%   $116.9638   $116.96   $116.95   $117.00  
  Purchase #4 $222.68   12.531%   $250.584   $250.58   $250.60   $250.60  
  Purchase #5 $14.26   5.239%   $15.0071   $15.01   $15.00   $15.00  
  Purchase #6 $183.75   10.329%   $202.7295   $202.73   $202.75   $202.70  
  Purchase #7 $197.76   5.680%   $208.9928   $208.99   $209.00   $209.00  
  7 purchase totals = $1,191.59       $1,301.9371   $1,301.93   $1,301.95   $1,302.00