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	$30.94	9.829%	$33.9811	$33.98	$34.00	$34.00
Purchase #2	$133.97	8.716%	$145.6468	$145.65	$145.65	$145.60
Purchase #3	$97.88	13.565%	$111.1574	$111.16	$111.15	$111.20
Purchase #4	$94.83	10.461%	$104.7502	$104.75	$104.75	$104.80
Purchase #5	$24.52	3.278%	$25.3238	$25.32	$25.30	$25.30
Purchase #6	$40.88	4.772%	$42.8308	$42.83	$42.85	$42.80
Purchase #7	$158.73	13.471%	$180.1125	$180.11	$180.10	$180.10
7 purchase totals =	$581.75		$643.8026	$643.80	$643.80	$643.80