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	$71.61	13.237%	$81.089	$81.09	$81.10	$81.10
Purchase #2	$49.38	8.291%	$53.4741	$53.47	$53.45	$53.50
Purchase #3	$246.42	10.147%	$271.4242	$271.42	$271.40	$271.40
Purchase #4	$139.92	9.246%	$152.857	$152.86	$152.85	$152.90
Purchase #5	$146.92	9.510%	$160.8921	$160.89	$160.90	$160.90
Purchase #6	$61.61	13.750%	$70.0814	$70.08	$70.10	$70.10
Purchase #7	$25.60	10.472%	$28.2808	$28.28	$28.30	$28.30
7 purchase totals =	$741.46		$818.0986	$818.09	$818.10	$818.20