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	$129.39	13.415%	$146.7477	$146.75	$146.75	$146.70
Purchase #2	$100.41	9.838%	$110.2883	$110.29	$110.30	$110.30
Purchase #3	$128.69	12.487%	$144.7595	$144.76	$144.75	$144.80
Purchase #4	$104.83	6.562%	$111.7089	$111.71	$111.70	$111.70
Purchase #5	$75.57	9.144%	$82.4801	$82.48	$82.50	$82.50
Purchase #6	$9.87	6.267%	$10.4886	$10.49	$10.50	$10.50
Purchase #7	$124.70	7.250%	$133.7408	$133.74	$133.75	$133.70
7 purchase totals =	$673.46		$740.2139	$740.22	$740.25	$740.20