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	$62.63	5.500%	$66.0747	$66.07	$66.05	$66.10
Purchase #2	$141.70	6.766%	$151.2874	$151.29	$151.30	$151.30
Purchase #3	$125.58	12.671%	$141.4922	$141.49	$141.50	$141.50
Purchase #4	$30.83	9.275%	$33.6895	$33.69	$33.70	$33.70
Purchase #5	$74.44	10.669%	$82.382	$82.38	$82.40	$82.40
Purchase #6	$43.93	3.136%	$45.3076	$45.31	$45.30	$45.30
Purchase #7	$151.89	10.866%	$168.3944	$168.39	$168.40	$168.40
7 purchase totals =	$631.00		$688.6278	$688.62	$688.65	$688.70