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 $104.25   13.156%   $117.9651   $117.97   $117.95   $118.00  
  Purchase #2 $66.54   9.186%   $72.6524   $72.65   $72.65   $72.70  
  Purchase #3 $109.50   9.352%   $119.7404   $119.74   $119.75   $119.70  
  Purchase #4 $107.61   6.372%   $114.4669   $114.47   $114.45   $114.50  
  Purchase #5 $99.26   4.782%   $104.0066   $104.01   $104.00   $104.00  
  Purchase #6 $5.31   11.648%   $5.9285   $5.93   $5.95   $5.90  
  Purchase #7 $192.60   8.176%   $208.347   $208.35   $208.35   $208.30  
  7 purchase totals = $685.07       $743.1069   $743.12   $743.10   $743.10