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	$80.51	11.278%	$89.5899	$89.59	$89.60	$89.60
Purchase #2	$201.86	13.750%	$229.6158	$229.62	$229.60	$229.60
Purchase #3	$250.76	11.381%	$279.299	$279.30	$279.30	$279.30
Purchase #4	$20.54	5.764%	$21.7239	$21.72	$21.70	$21.70
Purchase #5	$231.79	13.173%	$262.3237	$262.32	$262.30	$262.30
Purchase #6	$143.45	8.104%	$155.0752	$155.08	$155.10	$155.10
Purchase #7	$95.48	3.522%	$98.8428	$98.84	$98.85	$98.80
7 purchase totals =	$1,024.39		$1,136.4703	$1,136.47	$1,136.45	$1,136.40