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	$15.88	4.428%	$16.5832	$16.58	$16.60	$16.60
Purchase #2	$107.93	3.632%	$111.85	$111.85	$111.85	$111.90
Purchase #3	$20.50	5.795%	$21.688	$21.69	$21.70	$21.70
Purchase #4	$202.58	3.253%	$209.1699	$209.17	$209.15	$209.20
Purchase #5	$68.51	6.437%	$72.92	$72.92	$72.90	$72.90
Purchase #6	$35.45	7.549%	$38.1261	$38.13	$38.15	$38.10
Purchase #7	$98.77	13.141%	$111.7494	$111.75	$111.75	$111.70
7 purchase totals =	$549.62		$582.0866	$582.09	$582.10	$582.10