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	$143.74	4.720%	$150.5245	$150.52	$150.50	$150.50
Purchase #2	$104.52	3.384%	$108.057	$108.06	$108.05	$108.10
Purchase #3	$138.97	3.333%	$143.6019	$143.60	$143.60	$143.60
Purchase #4	$48.83	10.425%	$53.9205	$53.92	$53.90	$53.90
Purchase #5	$249.56	12.395%	$280.493	$280.49	$280.50	$280.50
Purchase #6	$49.68	11.543%	$55.4146	$55.41	$55.40	$55.40
Purchase #7	$70.78	13.759%	$80.5186	$80.52	$80.50	$80.50
7 purchase totals =	$806.08		$872.5301	$872.52	$872.45	$872.50