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	$183.75	13.813%	$209.1314	$209.13	$209.15	$209.10
Purchase #2	$123.64	3.342%	$127.772	$127.77	$127.75	$127.80
Purchase #3	$51.53	5.273%	$54.2472	$54.25	$54.25	$54.20
Purchase #4	$11.56	5.224%	$12.1639	$12.16	$12.15	$12.20
Purchase #5	$250.27	13.631%	$284.3843	$284.38	$284.40	$284.40
Purchase #6	$108.78	12.717%	$122.6136	$122.61	$122.60	$122.60
Purchase #7	$237.71	13.494%	$269.7866	$269.79	$269.80	$269.80
7 purchase totals =	$967.24		$1,080.0990	$1,080.09	$1,080.10	$1,080.10