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	$71.83	4.259%	$74.8892	$74.89	$74.90	$74.90
Purchase #2	$111.92	3.810%	$116.1842	$116.18	$116.20	$116.20
Purchase #3	$110.36	5.351%	$116.2654	$116.27	$116.25	$116.30
Purchase #4	$75.65	3.214%	$78.0814	$78.08	$78.10	$78.10
Purchase #5	$175.87	6.374%	$187.08	$187.08	$187.10	$187.10
Purchase #6	$91.70	8.435%	$99.4349	$99.43	$99.45	$99.40
Purchase #7	$49.64	5.724%	$52.4814	$52.48	$52.50	$52.50
7 purchase totals =	$686.97		$724.4165	$724.41	$724.50	$724.50