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 $243.26   10.309%   $268.3377   $268.34   $268.35   $268.30  
  Purchase #2 $124.29   7.593%   $133.7273   $133.73   $133.75   $133.70  
  Purchase #3 $111.64   6.765%   $119.1924   $119.19   $119.20   $119.20  
  Purchase #4 $64.66   11.707%   $72.2297   $72.23   $72.25   $72.20  
  Purchase #5 $151.61   5.348%   $159.7181   $159.72   $159.70   $159.70  
  Purchase #6 $42.44   6.202%   $45.0721   $45.07   $45.05   $45.10  
  Purchase #7 $230.91   7.570%   $248.3899   $248.39   $248.40   $248.40  
  7 purchase totals = $968.81       $1,046.6672   $1,046.67   $1,046.70   $1,046.60