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	$34.78	8.409%	$37.7047	$37.70	$37.70	$37.70
Purchase #2	$19.83	3.268%	$20.478	$20.48	$20.50	$20.50
Purchase #3	$119.78	10.406%	$132.2443	$132.24	$132.25	$132.20
Purchase #4	$174.35	9.839%	$191.5043	$191.50	$191.50	$191.50
Purchase #5	$60.83	11.168%	$67.6235	$67.62	$67.60	$67.60
Purchase #6	$155.86	7.164%	$167.0258	$167.03	$167.05	$167.00
Purchase #7	$138.47	12.131%	$155.2678	$155.27	$155.25	$155.30
7 purchase totals =	$703.90		$771.8484	$771.84	$771.85	$771.80