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	$129.52	3.245%	$133.7229	$133.72	$133.70	$133.70
Purchase #2	$52.37	13.701%	$59.5452	$59.55	$59.55	$59.50
Purchase #3	$46.78	11.399%	$52.1125	$52.11	$52.10	$52.10
Purchase #4	$89.69	12.505%	$100.9057	$100.91	$100.90	$100.90
Purchase #5	$221.49	5.844%	$234.4339	$234.43	$234.45	$234.40
Purchase #6	$145.95	8.260%	$158.0055	$158.01	$158.00	$158.00
Purchase #7	$37.59	9.296%	$41.0844	$41.08	$41.10	$41.10
7 purchase totals =	$723.39		$779.8101	$779.81	$779.80	$779.70