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	$204.45	12.841%	$230.7034	$230.70	$230.70	$230.70
Purchase #2	$40.28	4.222%	$41.9806	$41.98	$42.00	$42.00
Purchase #3	$180.51	3.845%	$187.4506	$187.45	$187.45	$187.50
Purchase #4	$18.68	4.689%	$19.5559	$19.56	$19.55	$19.60
Purchase #5	$85.89	4.732%	$89.9543	$89.95	$89.95	$90.00
Purchase #6	$29.72	8.142%	$32.1398	$32.14	$32.15	$32.10
Purchase #7	$57.75	8.615%	$62.7252	$62.73	$62.75	$62.70
7 purchase totals =	$617.28		$664.5098	$664.51	$664.55	$664.60