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	$180.78	13.478%	$205.1455	$205.15	$205.15	$205.10
Purchase #2	$55.49	9.385%	$60.6977	$60.70	$60.70	$60.70
Purchase #3	$138.62	5.113%	$145.7076	$145.71	$145.70	$145.70
Purchase #4	$84.78	13.453%	$96.1855	$96.19	$96.20	$96.20
Purchase #5	$97.91	13.729%	$111.3521	$111.35	$111.35	$111.40
Purchase #6	$111.91	13.571%	$127.0973	$127.10	$127.10	$127.10
Purchase #7	$94.74	10.319%	$104.5162	$104.52	$104.50	$104.50
7 purchase totals =	$764.23		$850.7019	$850.72	$850.70	$850.70