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	$77.32	7.586%	$83.1855	$83.19	$83.20	$83.20
Purchase #2	$98.42	4.791%	$103.1353	$103.14	$103.15	$103.10
Purchase #3	$102.47	9.195%	$111.8921	$111.89	$111.90	$111.90
Purchase #4	$231.34	9.435%	$253.1669	$253.17	$253.15	$253.20
Purchase #5	$75.72	11.834%	$84.6807	$84.68	$84.70	$84.70
Purchase #6	$51.73	5.514%	$54.5824	$54.58	$54.60	$54.60
Purchase #7	$166.48	7.384%	$178.7729	$178.77	$178.75	$178.80
7 purchase totals =	$803.48		$869.4158	$869.42	$869.45	$869.50