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	$10.99	10.415%	$12.1346	$12.13	$12.15	$12.10
Purchase #2	$247.86	11.848%	$277.2265	$277.23	$277.25	$277.20
Purchase #3	$158.39	6.283%	$168.3416	$168.34	$168.35	$168.30
Purchase #4	$71.59	4.181%	$74.5832	$74.58	$74.60	$74.60
Purchase #5	$131.84	12.586%	$148.4334	$148.43	$148.45	$148.40
Purchase #6	$233.52	8.460%	$253.2758	$253.28	$253.30	$253.30
Purchase #7	$190.82	3.172%	$196.8728	$196.87	$196.85	$196.90
7 purchase totals =	$1,045.01		$1,130.8679	$1,130.86	$1,130.95	$1,130.80