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	$247.28	7.274%	$265.2671	$265.27	$265.25	$265.30
Purchase #2	$104.77	6.621%	$111.7068	$111.71	$111.70	$111.70
Purchase #3	$205.31	5.699%	$217.0106	$217.01	$217.00	$217.00
Purchase #4	$226.63	13.148%	$256.4273	$256.43	$256.45	$256.40
Purchase #5	$103.29	5.492%	$108.9627	$108.96	$108.95	$109.00
Purchase #6	$208.92	11.830%	$233.6352	$233.64	$233.65	$233.60
Purchase #7	$157.47	9.289%	$172.0974	$172.10	$172.10	$172.10
7 purchase totals =	$1,253.67		$1,365.1071	$1,365.12	$1,365.10	$1,365.10