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	$213.53	13.459%	$242.269	$242.27	$242.25	$242.30
Purchase #2	$135.86	4.118%	$141.4547	$141.45	$141.45	$141.50
Purchase #3	$17.74	6.173%	$18.8351	$18.84	$18.85	$18.80
Purchase #4	$173.62	10.269%	$191.449	$191.45	$191.45	$191.40
Purchase #5	$204.98	10.773%	$227.0625	$227.06	$227.05	$227.10
Purchase #6	$62.82	4.422%	$65.5979	$65.60	$65.60	$65.60
Purchase #7	$9.95	5.704%	$10.5175	$10.52	$10.50	$10.50
7 purchase totals =	$818.50		$897.1857	$897.19	$897.15	$897.20