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	$95.93	4.447%	$100.196	$100.20	$100.20	$100.20
Purchase #2	$215.45	7.615%	$231.8565	$231.86	$231.85	$231.90
Purchase #3	$99.33	12.112%	$111.3608	$111.36	$111.35	$111.40
Purchase #4	$53.49	5.471%	$56.4164	$56.42	$56.40	$56.40
Purchase #5	$41.46	6.283%	$44.0649	$44.06	$44.05	$44.10
Purchase #6	$48.87	13.123%	$55.2832	$55.28	$55.30	$55.30
Purchase #7	$135.72	6.525%	$144.5757	$144.58	$144.60	$144.60
7 purchase totals =	$690.25		$743.7535	$743.76	$743.75	$743.90