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	$56.69	8.683%	$61.6124	$61.61	$61.60	$61.60
Purchase #2	$191.30	12.125%	$214.4951	$214.50	$214.50	$214.50
Purchase #3	$86.31	5.156%	$90.7601	$90.76	$90.75	$90.80
Purchase #4	$111.38	6.274%	$118.368	$118.37	$118.35	$118.40
Purchase #5	$51.37	9.600%	$56.3015	$56.30	$56.30	$56.30
Purchase #6	$145.68	3.439%	$150.6899	$150.69	$150.70	$150.70
Purchase #7	$100.68	11.459%	$112.2169	$112.22	$112.20	$112.20
7 purchase totals =	$743.41		$804.4439	$804.45	$804.40	$804.50