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	$50.87	7.421%	$54.6451	$54.65	$54.65	$54.60
Purchase #2	$250.87	7.537%	$269.7781	$269.78	$269.80	$269.80
Purchase #3	$134.28	6.169%	$142.5637	$142.56	$142.55	$142.60
Purchase #4	$78.34	12.171%	$87.8748	$87.87	$87.85	$87.90
Purchase #5	$155.86	3.314%	$161.0252	$161.03	$161.05	$161.00
Purchase #6	$46.33	3.788%	$48.085	$48.09	$48.10	$48.10
Purchase #7	$53.69	10.767%	$59.4708	$59.47	$59.45	$59.50
7 purchase totals =	$770.24		$823.4427	$823.45	$823.45	$823.50