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	$65.55	13.136%	$74.1606	$74.16	$74.15	$74.20
Purchase #2	$166.34	4.427%	$173.7039	$173.70	$173.70	$173.70
Purchase #3	$114.55	12.294%	$128.6328	$128.63	$128.65	$128.60
Purchase #4	$29.69	10.339%	$32.7596	$32.76	$32.75	$32.80
Purchase #5	$151.78	10.565%	$167.8156	$167.82	$167.80	$167.80
Purchase #6	$144.83	5.672%	$153.0448	$153.04	$153.05	$153.00
Purchase #7	$83.52	7.401%	$89.7013	$89.70	$89.70	$89.70
7 purchase totals =	$756.26		$819.8186	$819.81	$819.80	$819.80