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 $221.66   10.648%   $245.2624   $245.26   $245.25   $245.30  
  Purchase #2 $202.25   3.319%   $208.9627   $208.96   $208.95   $209.00  
  Purchase #3 $79.90   8.863%   $86.9815   $86.98   $87.00   $87.00  
  Purchase #4 $244.89   7.584%   $263.4625   $263.46   $263.45   $263.50  
  Purchase #5 $23.64   8.609%   $25.6752   $25.68   $25.70   $25.70  
  Purchase #6 $9.29   6.678%   $9.9104   $9.91   $9.90   $9.90  
  Purchase #7 $215.31   5.647%   $227.4686   $227.47   $227.45   $227.50  
  7 purchase totals = $996.94       $1,067.7233   $1,067.72   $1,067.70   $1,067.90