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	$48.56	6.135%	$51.5392	$51.54	$51.55	$51.50
Purchase #2	$72.36	13.166%	$81.8869	$81.89	$81.90	$81.90
Purchase #3	$48.65	8.465%	$52.7682	$52.77	$52.75	$52.80
Purchase #4	$112.79	4.857%	$118.2682	$118.27	$118.25	$118.30
Purchase #5	$133.87	8.598%	$145.3801	$145.38	$145.40	$145.40
Purchase #6	$204.98	4.794%	$214.8067	$214.81	$214.80	$214.80
Purchase #7	$127.39	11.822%	$142.45	$142.45	$142.45	$142.50
7 purchase totals =	$748.60		$807.0993	$807.11	$807.10	$807.20