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 $235.93   11.613%   $263.3286   $263.33   $263.35   $263.30  
  Purchase #2 $175.72   9.630%   $192.6418   $192.64   $192.65   $192.60  
  Purchase #3 $178.54   10.485%   $197.2599   $197.26   $197.25   $197.30  
  Purchase #4 $115.65   10.444%   $127.7285   $127.73   $127.75   $127.70  
  Purchase #5 $8.76   6.185%   $9.3018   $9.30   $9.30   $9.30  
  Purchase #6 $200.78   3.736%   $208.2811   $208.28   $208.30   $208.30  
  Purchase #7 $170.26   8.694%   $185.0624   $185.06   $185.05   $185.10  
  7 purchase totals = $1,085.64       $1,183.6041   $1,183.60   $1,183.65   $1,183.60