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	$76.52	6.697%	$81.6445	$81.64	$81.65	$81.60
Purchase #2	$17.38	4.808%	$18.2156	$18.22	$18.20	$18.20
Purchase #3	$21.55	8.841%	$23.4552	$23.46	$23.45	$23.50
Purchase #4	$39.93	9.329%	$43.6551	$43.66	$43.65	$43.70
Purchase #5	$207.29	6.606%	$220.9836	$220.98	$221.00	$221.00
Purchase #6	$100.30	11.327%	$111.661	$111.66	$111.65	$111.70
Purchase #7	$128.48	8.666%	$139.6141	$139.61	$139.60	$139.60
7 purchase totals =	$591.45		$639.2291	$639.23	$639.20	$639.30