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	$57.54	13.186%	$65.1272	$65.13	$65.15	$65.10
Purchase #2	$242.28	6.238%	$257.3934	$257.39	$257.40	$257.40
Purchase #3	$48.82	11.539%	$54.4533	$54.45	$54.45	$54.50
Purchase #4	$212.73	8.486%	$230.7823	$230.78	$230.80	$230.80
Purchase #5	$41.80	3.277%	$43.1698	$43.17	$43.15	$43.20
Purchase #6	$12.28	4.839%	$12.8742	$12.87	$12.85	$12.90
Purchase #7	$47.43	9.219%	$51.8026	$51.80	$51.80	$51.80
7 purchase totals =	$662.88		$715.6028	$715.59	$715.60	$715.70