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	$64.57	9.126%	$70.4627	$70.46	$70.45	$70.50
Purchase #2	$226.94	12.462%	$255.2213	$255.22	$255.20	$255.20
Purchase #3	$210.83	4.830%	$221.0131	$221.01	$221.00	$221.00
Purchase #4	$75.46	5.303%	$79.4616	$79.46	$79.45	$79.50
Purchase #5	$136.84	12.191%	$153.5222	$153.52	$153.50	$153.50
Purchase #6	$98.37	10.642%	$108.8385	$108.84	$108.85	$108.80
Purchase #7	$82.34	9.149%	$89.8733	$89.87	$89.85	$89.90
7 purchase totals =	$895.35		$978.3927	$978.38	$978.30	$978.40