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	$115.59	11.185%	$128.5187	$128.52	$128.50	$128.50
Purchase #2	$161.29	7.727%	$173.7529	$173.75	$173.75	$173.80
Purchase #3	$94.52	11.230%	$105.1346	$105.13	$105.15	$105.10
Purchase #4	$242.88	5.795%	$256.9549	$256.95	$256.95	$257.00
Purchase #5	$170.36	6.162%	$180.8576	$180.86	$180.85	$180.90
Purchase #6	$15.42	11.169%	$17.1423	$17.14	$17.15	$17.10
Purchase #7	$127.89	8.755%	$139.0868	$139.09	$139.10	$139.10
7 purchase totals =	$927.95		$1,001.4478	$1,001.44	$1,001.45	$1,001.50