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	$64.74	4.401%	$67.5892	$67.59	$67.60	$67.60
Purchase #2	$132.34	9.253%	$144.5854	$144.59	$144.60	$144.60
Purchase #3	$41.74	10.836%	$46.2629	$46.26	$46.25	$46.30
Purchase #4	$191.76	12.572%	$215.8681	$215.87	$215.85	$215.90
Purchase #5	$17.59	3.239%	$18.1597	$18.16	$18.15	$18.20
Purchase #6	$137.87	4.853%	$144.5608	$144.56	$144.55	$144.60
Purchase #7	$112.58	13.167%	$127.4034	$127.40	$127.40	$127.40
7 purchase totals =	$698.62		$764.4295	$764.43	$764.40	$764.60