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 $191.38   6.170%   $203.1881   $203.19   $203.20   $203.20  
  Purchase #2 $132.44   6.793%   $141.4366   $141.44   $141.45   $141.40  
  Purchase #3 $79.32   3.622%   $82.193   $82.19   $82.20   $82.20  
  Purchase #4 $242.38   10.748%   $268.431   $268.43   $268.45   $268.40  
  Purchase #5 $65.32   11.548%   $72.8632   $72.86   $72.85   $72.90  
  Purchase #6 $248.99   11.364%   $277.2852   $277.29   $277.30   $277.30  
  Purchase #7 $230.76   9.458%   $252.5853   $252.59   $252.60   $252.60  
  7 purchase totals = $1,190.59       $1,297.9824   $1,297.99   $1,298.05   $1,298.00