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	$12.26	4.327%	$12.7905	$12.79	$12.80	$12.80
Purchase #2	$136.61	13.566%	$155.1425	$155.14	$155.15	$155.10
Purchase #3	$145.30	5.451%	$153.2203	$153.22	$153.20	$153.20
Purchase #4	$182.49	7.605%	$196.3684	$196.37	$196.35	$196.40
Purchase #5	$99.29	12.463%	$111.6645	$111.66	$111.65	$111.70
Purchase #6	$183.88	9.239%	$200.8687	$200.87	$200.85	$200.90
Purchase #7	$94.92	5.727%	$100.3561	$100.36	$100.35	$100.40
7 purchase totals =	$854.75		$930.4110	$930.41	$930.35	$930.50