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	$25.64	11.784%	$28.6614	$28.66	$28.65	$28.70
Purchase #2	$230.33	12.136%	$258.2828	$258.28	$258.30	$258.30
Purchase #3	$55.71	10.144%	$61.3612	$61.36	$61.35	$61.40
Purchase #4	$216.72	6.177%	$230.1068	$230.11	$230.10	$230.10
Purchase #5	$10.27	5.547%	$10.8397	$10.84	$10.85	$10.80
Purchase #6	$53.38	8.339%	$57.8314	$57.83	$57.85	$57.80
Purchase #7	$18.38	5.733%	$19.4337	$19.43	$19.45	$19.40
7 purchase totals =	$610.43		$666.5170	$666.51	$666.55	$666.50