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	$92.88	7.733%	$100.0624	$100.06	$100.05	$100.10
Purchase #2	$184.99	6.443%	$196.9089	$196.91	$196.90	$196.90
Purchase #3	$108.38	9.634%	$118.8213	$118.82	$118.80	$118.80
Purchase #4	$53.67	11.788%	$59.9966	$60.00	$60.00	$60.00
Purchase #5	$22.35	5.505%	$23.5804	$23.58	$23.60	$23.60
Purchase #6	$91.57	12.830%	$103.3184	$103.32	$103.30	$103.30
Purchase #7	$235.57	13.693%	$267.8266	$267.83	$267.85	$267.80
7 purchase totals =	$789.41		$870.5146	$870.52	$870.50	$870.50