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	$50.91	10.674%	$56.3441	$56.34	$56.35	$56.30
Purchase #2	$120.68	9.196%	$131.7777	$131.78	$131.80	$131.80
Purchase #3	$195.86	4.752%	$205.1673	$205.17	$205.15	$205.20
Purchase #4	$46.35	12.724%	$52.2476	$52.25	$52.25	$52.20
Purchase #5	$132.88	9.418%	$145.3946	$145.39	$145.40	$145.40
Purchase #6	$216.54	3.304%	$223.6945	$223.69	$223.70	$223.70
Purchase #7	$73.78	4.763%	$77.2941	$77.29	$77.30	$77.30
7 purchase totals =	$837.00		$891.9199	$891.91	$891.95	$891.90