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	$179.56	5.528%	$189.4861	$189.49	$189.50	$189.50
Purchase #2	$64.77	4.393%	$67.6153	$67.62	$67.60	$67.60
Purchase #3	$104.43	7.519%	$112.2821	$112.28	$112.30	$112.30
Purchase #4	$29.78	8.397%	$32.2806	$32.28	$32.30	$32.30
Purchase #5	$126.81	13.424%	$143.833	$143.83	$143.85	$143.80
Purchase #6	$160.74	9.777%	$176.4555	$176.46	$176.45	$176.50
Purchase #7	$101.88	9.456%	$111.5138	$111.51	$111.50	$111.50
7 purchase totals =	$767.97		$833.4664	$833.47	$833.50	$833.50