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	$118.43	11.104%	$131.5805	$131.58	$131.60	$131.60
Purchase #2	$56.59	12.123%	$63.4504	$63.45	$63.45	$63.50
Purchase #3	$211.39	11.304%	$235.2855	$235.29	$235.30	$235.30
Purchase #4	$141.40	6.521%	$150.6207	$150.62	$150.60	$150.60
Purchase #5	$51.70	10.486%	$57.1213	$57.12	$57.10	$57.10
Purchase #6	$48.29	3.521%	$49.9903	$49.99	$50.00	$50.00
Purchase #7	$84.58	6.613%	$90.1733	$90.17	$90.15	$90.20
7 purchase totals =	$712.38		$778.2220	$778.22	$778.20	$778.30