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	$45.60	12.483%	$51.2922	$51.29	$51.30	$51.30
Purchase #2	$151.91	9.645%	$166.5617	$166.56	$166.55	$166.60
Purchase #3	$28.51	13.231%	$32.2822	$32.28	$32.30	$32.30
Purchase #4	$133.38	9.238%	$145.7016	$145.70	$145.70	$145.70
Purchase #5	$60.27	10.283%	$66.4676	$66.47	$66.45	$66.50
Purchase #6	$76.73	3.465%	$79.3887	$79.39	$79.40	$79.40
Purchase #7	$124.94	4.545%	$130.6185	$130.62	$130.60	$130.60
7 purchase totals =	$621.34		$672.3125	$672.31	$672.30	$672.40