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	$179.78	3.599%	$186.2503	$186.25	$186.25	$186.30
Purchase #2	$99.62	3.692%	$103.298	$103.30	$103.30	$103.30
Purchase #3	$177.86	12.262%	$199.6692	$199.67	$199.65	$199.70
Purchase #4	$61.40	8.307%	$66.5005	$66.50	$66.50	$66.50
Purchase #5	$89.71	11.629%	$100.1424	$100.14	$100.15	$100.10
Purchase #6	$155.42	11.477%	$173.2576	$173.26	$173.25	$173.30
Purchase #7	$9.96	8.153%	$10.772	$10.77	$10.75	$10.80
7 purchase totals =	$773.75		$839.8900	$839.89	$839.85	$840.00