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	$29.52	12.335%	$33.1613	$33.16	$33.15	$33.20
Purchase #2	$213.80	5.161%	$224.8342	$224.83	$224.85	$224.80
Purchase #3	$7.30	12.148%	$8.1868	$8.19	$8.20	$8.20
Purchase #4	$145.82	8.639%	$158.4174	$158.42	$158.40	$158.40
Purchase #5	$46.60	3.825%	$48.3825	$48.38	$48.40	$48.40
Purchase #6	$212.52	12.233%	$238.5176	$238.52	$238.50	$238.50
Purchase #7	$71.25	8.862%	$77.5642	$77.56	$77.55	$77.60
7 purchase totals =	$726.81		$789.0640	$789.06	$789.05	$789.10