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	$228.82	4.158%	$238.3343	$238.33	$238.35	$238.30
Purchase #2	$80.94	10.778%	$89.6637	$89.66	$89.65	$89.70
Purchase #3	$158.38	10.357%	$174.7834	$174.78	$174.80	$174.80
Purchase #4	$212.55	3.271%	$219.5025	$219.50	$219.50	$219.50
Purchase #5	$210.64	5.820%	$222.8992	$222.90	$222.90	$222.90
Purchase #6	$218.48	9.688%	$239.6463	$239.65	$239.65	$239.60
Purchase #7	$138.25	4.470%	$144.4298	$144.43	$144.45	$144.40
7 purchase totals =	$1,248.06		$1,329.2592	$1,329.25	$1,329.30	$1,329.20