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	$103.37	4.854%	$108.3876	$108.39	$108.40	$108.40
Purchase #2	$129.63	6.834%	$138.4889	$138.49	$138.50	$138.50
Purchase #3	$117.49	8.292%	$127.2323	$127.23	$127.25	$127.20
Purchase #4	$133.65	4.623%	$139.8286	$139.83	$139.85	$139.80
Purchase #5	$124.64	10.329%	$137.5141	$137.51	$137.50	$137.50
Purchase #6	$150.62	12.216%	$169.0197	$169.02	$169.00	$169.00
Purchase #7	$123.49	12.787%	$139.2807	$139.28	$139.30	$139.30
7 purchase totals =	$882.89		$959.7519	$959.75	$959.80	$959.70