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	$100.30	5.483%	$105.7994	$105.80	$105.80	$105.80
Purchase #2	$180.66	5.631%	$190.833	$190.83	$190.85	$190.80
Purchase #3	$14.40	7.599%	$15.4943	$15.49	$15.50	$15.50
Purchase #4	$130.30	11.434%	$145.1985	$145.20	$145.20	$145.20
Purchase #5	$224.78	13.501%	$255.1275	$255.13	$255.15	$255.10
Purchase #6	$122.67	13.530%	$139.2673	$139.27	$139.25	$139.30
Purchase #7	$68.34	10.807%	$75.7255	$75.73	$75.75	$75.70
7 purchase totals =	$841.45		$927.4455	$927.45	$927.50	$927.40