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	$230.71	5.589%	$243.6044	$243.60	$243.60	$243.60
Purchase #2	$183.32	12.145%	$205.5842	$205.58	$205.60	$205.60
Purchase #3	$242.54	5.867%	$256.7698	$256.77	$256.75	$256.80
Purchase #4	$152.37	9.226%	$166.4277	$166.43	$166.45	$166.40
Purchase #5	$111.83	13.446%	$126.8667	$126.87	$126.85	$126.90
Purchase #6	$24.77	13.728%	$28.1704	$28.17	$28.15	$28.20
Purchase #7	$49.97	9.493%	$54.7137	$54.71	$54.70	$54.70
7 purchase totals =	$995.51		$1,082.1369	$1,082.13	$1,082.10	$1,082.20