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	$150.51	5.210%	$158.3516	$158.35	$158.35	$158.40
Purchase #2	$114.82	4.845%	$120.383	$120.38	$120.40	$120.40
Purchase #3	$141.75	6.231%	$150.5824	$150.58	$150.60	$150.60
Purchase #4	$53.60	11.305%	$59.6595	$59.66	$59.65	$59.70
Purchase #5	$39.78	8.345%	$43.0996	$43.10	$43.10	$43.10
Purchase #6	$121.43	13.728%	$138.0999	$138.10	$138.10	$138.10
Purchase #7	$62.68	9.237%	$68.4698	$68.47	$68.45	$68.50
7 purchase totals =	$684.57		$738.6458	$738.64	$738.65	$738.80