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	$103.52	9.786%	$113.6505	$113.65	$113.65	$113.70
Purchase #2	$72.42	12.671%	$81.5963	$81.60	$81.60	$81.60
Purchase #3	$160.72	7.175%	$172.2517	$172.25	$172.25	$172.30
Purchase #4	$114.45	11.664%	$127.7994	$127.80	$127.80	$127.80
Purchase #5	$156.77	5.308%	$165.0914	$165.09	$165.10	$165.10
Purchase #6	$52.59	4.309%	$54.8561	$54.86	$54.85	$54.90
Purchase #7	$85.73	4.843%	$89.8819	$89.88	$89.90	$89.90
7 purchase totals =	$746.20		$805.1273	$805.13	$805.15	$805.30