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	$160.55	11.813%	$179.5158	$179.52	$179.50	$179.50
Purchase #2	$57.34	12.575%	$64.5505	$64.55	$64.55	$64.60
Purchase #3	$16.85	10.501%	$18.6194	$18.62	$18.60	$18.60
Purchase #4	$132.39	10.801%	$146.6894	$146.69	$146.70	$146.70
Purchase #5	$102.51	8.456%	$111.1782	$111.18	$111.20	$111.20
Purchase #6	$239.84	13.693%	$272.6813	$272.68	$272.70	$272.70
Purchase #7	$57.72	5.302%	$60.7803	$60.78	$60.80	$60.80
7 purchase totals =	$767.20		$854.0149	$854.02	$854.05	$854.10