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 $14.32   11.302%   $15.9384   $15.94   $15.95   $15.90  
  Purchase #2 $227.35   4.440%   $237.4443   $237.44   $237.45   $237.40  
  Purchase #3 $42.32   6.216%   $44.9506   $44.95   $44.95   $45.00  
  Purchase #4 $152.41   9.409%   $166.7503   $166.75   $166.75   $166.80  
  Purchase #5 $52.54   5.397%   $55.3756   $55.38   $55.40   $55.40  
  Purchase #6 $248.99   10.739%   $275.729   $275.73   $275.75   $275.70  
  Purchase #7 $130.27   8.622%   $141.5019   $141.50   $141.50   $141.50  
  7 purchase totals = $868.20       $937.6901   $937.69   $937.75   $937.70