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	$231.51	9.103%	$252.5844	$252.58	$252.60	$252.60
Purchase #2	$149.74	4.327%	$156.2192	$156.22	$156.20	$156.20
Purchase #3	$97.59	4.365%	$101.8498	$101.85	$101.85	$101.80
Purchase #4	$178.80	3.788%	$185.5729	$185.57	$185.55	$185.60
Purchase #5	$92.50	12.763%	$104.3058	$104.31	$104.30	$104.30
Purchase #6	$56.89	10.462%	$62.8418	$62.84	$62.85	$62.80
Purchase #7	$49.59	7.155%	$53.1382	$53.14	$53.15	$53.10
7 purchase totals =	$856.62		$916.5121	$916.51	$916.50	$916.40