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	$92.80	8.404%	$100.5989	$100.60	$100.60	$100.60
Purchase #2	$144.82	9.133%	$158.0464	$158.05	$158.05	$158.00
Purchase #3	$41.62	9.412%	$45.5373	$45.54	$45.55	$45.50
Purchase #4	$45.98	7.759%	$49.5476	$49.55	$49.55	$49.50
Purchase #5	$190.39	7.739%	$205.1243	$205.12	$205.10	$205.10
Purchase #6	$123.52	13.300%	$139.9482	$139.95	$139.95	$139.90
Purchase #7	$95.62	8.682%	$103.9217	$103.92	$103.90	$103.90
7 purchase totals =	$734.75		$802.7244	$802.73	$802.70	$802.50