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	$230.25	11.542%	$256.8255	$256.83	$256.85	$256.80
Purchase #2	$94.88	5.395%	$99.9988	$100.00	$100.00	$100.00
Purchase #3	$63.60	10.558%	$70.3149	$70.31	$70.30	$70.30
Purchase #4	$238.67	5.826%	$252.5749	$252.57	$252.55	$252.60
Purchase #5	$107.52	3.442%	$111.2208	$111.22	$111.20	$111.20
Purchase #6	$165.84	3.822%	$172.1784	$172.18	$172.20	$172.20
Purchase #7	$114.54	8.686%	$124.4889	$124.49	$124.50	$124.50
7 purchase totals =	$1,015.30		$1,087.6022	$1,087.60	$1,087.60	$1,087.60