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	$123.52	5.384%	$130.1703	$130.17	$130.15	$130.20
Purchase #2	$120.89	11.508%	$134.802	$134.80	$134.80	$134.80
Purchase #3	$46.80	10.139%	$51.5451	$51.55	$51.55	$51.50
Purchase #4	$145.90	8.855%	$158.8194	$158.82	$158.80	$158.80
Purchase #5	$138.46	11.671%	$154.6197	$154.62	$154.60	$154.60
Purchase #6	$37.88	6.169%	$40.2168	$40.22	$40.20	$40.20
Purchase #7	$191.45	3.706%	$198.5451	$198.55	$198.55	$198.50
7 purchase totals =	$804.90		$868.7184	$868.73	$868.65	$868.60