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	$166.78	3.873%	$173.2394	$173.24	$173.25	$173.20
Purchase #2	$128.34	11.329%	$142.8796	$142.88	$142.90	$142.90
Purchase #3	$131.95	8.675%	$143.3967	$143.40	$143.40	$143.40
Purchase #4	$41.38	3.670%	$42.8986	$42.90	$42.90	$42.90
Purchase #5	$19.93	8.644%	$21.6527	$21.65	$21.65	$21.70
Purchase #6	$24.47	13.835%	$27.8554	$27.86	$27.85	$27.90
Purchase #7	$87.98	9.303%	$96.1648	$96.16	$96.15	$96.20
7 purchase totals =	$600.83		$648.0872	$648.09	$648.10	$648.20