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	$226.81	13.222%	$256.7988	$256.80	$256.80	$256.80
Purchase #2	$193.78	10.766%	$214.6424	$214.64	$214.65	$214.60
Purchase #3	$84.84	6.807%	$90.6151	$90.62	$90.60	$90.60
Purchase #4	$54.37	12.585%	$61.2125	$61.21	$61.20	$61.20
Purchase #5	$11.45	6.234%	$12.1638	$12.16	$12.15	$12.20
Purchase #6	$166.25	3.613%	$172.2566	$172.26	$172.25	$172.30
Purchase #7	$156.82	3.665%	$162.5675	$162.57	$162.55	$162.60
7 purchase totals =	$894.32		$970.2567	$970.26	$970.20	$970.30