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	$115.73	13.520%	$131.3767	$131.38	$131.40	$131.40
Purchase #2	$48.30	7.789%	$52.0621	$52.06	$52.05	$52.10
Purchase #3	$207.66	11.186%	$230.8888	$230.89	$230.90	$230.90
Purchase #4	$154.60	7.546%	$166.2661	$166.27	$166.25	$166.30
Purchase #5	$151.72	13.244%	$171.8138	$171.81	$171.80	$171.80
Purchase #6	$107.47	10.485%	$118.7382	$118.74	$118.75	$118.70
Purchase #7	$174.42	8.435%	$189.1323	$189.13	$189.15	$189.10
7 purchase totals =	$959.90		$1,060.2780	$1,060.28	$1,060.30	$1,060.30