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	$233.47	11.866%	$261.1736	$261.17	$261.15	$261.20
Purchase #2	$177.30	3.657%	$183.7839	$183.78	$183.80	$183.80
Purchase #3	$61.84	7.494%	$66.4743	$66.47	$66.45	$66.50
Purchase #4	$129.49	7.819%	$139.6148	$139.61	$139.60	$139.60
Purchase #5	$169.94	9.725%	$186.4667	$186.47	$186.45	$186.50
Purchase #6	$172.42	4.849%	$180.7806	$180.78	$180.80	$180.80
Purchase #7	$49.81	6.208%	$52.9022	$52.90	$52.90	$52.90
7 purchase totals =	$994.27		$1,071.1961	$1,071.18	$1,071.15	$1,071.30