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	$99.30	12.405%	$111.6182	$111.62	$111.60	$111.60
Purchase #2	$44.85	10.353%	$49.4933	$49.49	$49.50	$49.50
Purchase #3	$99.45	4.679%	$104.1033	$104.10	$104.10	$104.10
Purchase #4	$47.41	7.143%	$50.7965	$50.80	$50.80	$50.80
Purchase #5	$207.42	13.713%	$235.8635	$235.86	$235.85	$235.90
Purchase #6	$138.41	8.425%	$150.071	$150.07	$150.05	$150.10
Purchase #7	$95.94	4.203%	$99.9724	$99.97	$99.95	$100.00
7 purchase totals =	$732.78		$801.9182	$801.91	$801.85	$802.00