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	$149.82	5.845%	$158.577	$158.58	$158.60	$158.60
Purchase #2	$95.48	9.832%	$104.8676	$104.87	$104.85	$104.90
Purchase #3	$66.35	9.273%	$72.5026	$72.50	$72.50	$72.50
Purchase #4	$205.32	11.254%	$228.4267	$228.43	$228.45	$228.40
Purchase #5	$137.37	11.254%	$152.8296	$152.83	$152.85	$152.80
Purchase #6	$101.84	4.367%	$106.2874	$106.29	$106.30	$106.30
Purchase #7	$135.38	5.593%	$142.9518	$142.95	$142.95	$143.00
7 purchase totals =	$891.56		$966.4427	$966.45	$966.50	$966.50