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	$56.43	6.608%	$60.1589	$60.16	$60.15	$60.20
Purchase #2	$127.46	9.516%	$139.5891	$139.59	$139.60	$139.60
Purchase #3	$53.57	11.191%	$59.565	$59.57	$59.55	$59.60
Purchase #4	$11.49	12.713%	$12.9507	$12.95	$12.95	$13.00
Purchase #5	$143.98	10.315%	$158.8315	$158.83	$158.85	$158.80
Purchase #6	$224.29	13.389%	$254.3202	$254.32	$254.30	$254.30
Purchase #7	$226.97	10.859%	$251.6167	$251.62	$251.60	$251.60
7 purchase totals =	$844.19		$937.0321	$937.04	$937.00	$937.10