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	$52.48	9.366%	$57.3953	$57.40	$57.40	$57.40
Purchase #2	$19.69	3.836%	$20.4453	$20.45	$20.45	$20.40
Purchase #3	$122.93	4.818%	$128.8528	$128.85	$128.85	$128.90
Purchase #4	$38.71	10.577%	$42.8044	$42.80	$42.80	$42.80
Purchase #5	$25.81	13.313%	$29.2461	$29.25	$29.25	$29.20
Purchase #6	$79.94	8.406%	$86.6598	$86.66	$86.65	$86.70
Purchase #7	$115.70	10.528%	$127.8809	$127.88	$127.90	$127.90
7 purchase totals =	$455.26		$493.2846	$493.29	$493.30	$493.30