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	$10.97	12.363%	$12.3262	$12.33	$12.35	$12.30
Purchase #2	$25.26	10.431%	$27.8949	$27.89	$27.90	$27.90
Purchase #3	$111.92	8.223%	$121.1232	$121.12	$121.10	$121.10
Purchase #4	$158.39	9.138%	$172.8637	$172.86	$172.85	$172.90
Purchase #5	$146.95	4.679%	$153.8258	$153.83	$153.85	$153.80
Purchase #6	$103.72	8.630%	$112.671	$112.67	$112.65	$112.70
Purchase #7	$31.74	12.868%	$35.8243	$35.82	$35.80	$35.80
7 purchase totals =	$588.95		$636.5291	$636.52	$636.50	$636.50