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	$26.28	6.778%	$28.0613	$28.06	$28.05	$28.10
Purchase #2	$11.85	4.806%	$12.4195	$12.42	$12.40	$12.40
Purchase #3	$222.50	8.294%	$240.9542	$240.95	$240.95	$241.00
Purchase #4	$75.39	4.486%	$78.772	$78.77	$78.75	$78.80
Purchase #5	$240.69	6.563%	$256.4865	$256.49	$256.50	$256.50
Purchase #6	$132.96	6.410%	$141.4827	$141.48	$141.50	$141.50
Purchase #7	$101.68	4.674%	$106.4325	$106.43	$106.45	$106.40
7 purchase totals =	$811.35		$864.6087	$864.60	$864.60	$864.70