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	$141.42	10.512%	$156.2861	$156.29	$156.30	$156.30
Purchase #2	$88.55	13.231%	$100.2661	$100.27	$100.25	$100.30
Purchase #3	$62.65	6.736%	$66.8701	$66.87	$66.85	$66.90
Purchase #4	$204.45	4.750%	$214.1614	$214.16	$214.15	$214.20
Purchase #5	$18.28	11.740%	$20.4261	$20.43	$20.45	$20.40
Purchase #6	$47.36	13.671%	$53.8346	$53.83	$53.85	$53.80
Purchase #7	$194.92	13.635%	$221.4973	$221.50	$221.50	$221.50
7 purchase totals =	$757.63		$833.3417	$833.35	$833.35	$833.40