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	$128.80	5.707%	$136.1506	$136.15	$136.15	$136.20
Purchase #2	$13.60	9.643%	$14.9114	$14.91	$14.90	$14.90
Purchase #3	$203.82	12.444%	$229.1834	$229.18	$229.20	$229.20
Purchase #4	$57.65	3.251%	$59.5242	$59.52	$59.50	$59.50
Purchase #5	$178.60	12.422%	$200.7857	$200.79	$200.80	$200.80
Purchase #6	$81.85	13.152%	$92.6149	$92.61	$92.60	$92.60
Purchase #7	$190.73	4.104%	$198.5576	$198.56	$198.55	$198.60
7 purchase totals =	$855.05		$931.7278	$931.72	$931.70	$931.80