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	$225.54	10.194%	$248.5315	$248.53	$248.55	$248.50
Purchase #2	$249.39	10.719%	$276.1221	$276.12	$276.10	$276.10
Purchase #3	$99.78	11.820%	$111.574	$111.57	$111.55	$111.60
Purchase #4	$15.45	4.420%	$16.1329	$16.13	$16.15	$16.10
Purchase #5	$42.43	7.362%	$45.5537	$45.55	$45.55	$45.60
Purchase #6	$61.75	11.150%	$68.6351	$68.64	$68.65	$68.60
Purchase #7	$126.54	13.737%	$143.9228	$143.92	$143.90	$143.90
7 purchase totals =	$820.88		$910.4721	$910.46	$910.45	$910.40