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	$100.30	11.379%	$111.7131	$111.71	$111.70	$111.70
Purchase #2	$82.92	9.201%	$90.5495	$90.55	$90.55	$90.50
Purchase #3	$207.57	3.415%	$214.6585	$214.66	$214.65	$214.70
Purchase #4	$19.48	13.119%	$22.0356	$22.04	$22.05	$22.00
Purchase #5	$116.43	11.123%	$129.3805	$129.38	$129.40	$129.40
Purchase #6	$159.87	6.718%	$170.6101	$170.61	$170.60	$170.60
Purchase #7	$38.93	11.388%	$43.3633	$43.36	$43.35	$43.40
7 purchase totals =	$725.50		$782.3106	$782.31	$782.30	$782.30