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	$66.55	5.759%	$70.3826	$70.38	$70.40	$70.40
Purchase #2	$44.77	12.653%	$50.4347	$50.43	$50.45	$50.40
Purchase #3	$211.93	13.846%	$241.2738	$241.27	$241.25	$241.30
Purchase #4	$141.69	4.762%	$148.4373	$148.44	$148.45	$148.40
Purchase #5	$154.39	8.565%	$167.6135	$167.61	$167.60	$167.60
Purchase #6	$19.94	6.733%	$21.2826	$21.28	$21.30	$21.30
Purchase #7	$104.29	13.823%	$118.706	$118.71	$118.70	$118.70
7 purchase totals =	$743.56		$818.1305	$818.12	$818.15	$818.10