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	$40.88	4.395%	$42.6767	$42.68	$42.70	$42.70
Purchase #2	$154.93	7.104%	$165.9362	$165.94	$165.95	$165.90
Purchase #3	$132.57	3.700%	$137.4751	$137.48	$137.50	$137.50
Purchase #4	$77.46	3.708%	$80.3322	$80.33	$80.35	$80.30
Purchase #5	$91.86	9.342%	$100.4416	$100.44	$100.45	$100.40
Purchase #6	$18.70	10.201%	$20.6076	$20.61	$20.60	$20.60
Purchase #7	$48.85	6.114%	$51.8367	$51.84	$51.85	$51.80
7 purchase totals =	$565.25		$599.3061	$599.32	$599.40	$599.20