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	$30.98	12.450%	$34.837	$34.84	$34.85	$34.80
Purchase #2	$144.66	9.671%	$158.6501	$158.65	$158.65	$158.70
Purchase #3	$52.43	8.178%	$56.7177	$56.72	$56.70	$56.70
Purchase #4	$33.36	11.351%	$37.1467	$37.15	$37.15	$37.10
Purchase #5	$29.76	5.626%	$31.4343	$31.43	$31.45	$31.40
Purchase #6	$40.69	4.700%	$42.6024	$42.60	$42.60	$42.60
Purchase #7	$232.28	10.565%	$256.8204	$256.82	$256.80	$256.80
7 purchase totals =	$564.16		$618.2086	$618.21	$618.20	$618.10