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	$144.35	10.149%	$159.0001	$159.00	$159.00	$159.00
Purchase #2	$104.86	6.269%	$111.4337	$111.43	$111.45	$111.40
Purchase #3	$143.87	10.303%	$158.6929	$158.69	$158.70	$158.70
Purchase #4	$76.70	12.401%	$86.2116	$86.21	$86.20	$86.20
Purchase #5	$37.47	13.572%	$42.5554	$42.56	$42.55	$42.60
Purchase #6	$250.91	5.608%	$264.981	$264.98	$265.00	$265.00
Purchase #7	$19.63	10.275%	$21.647	$21.65	$21.65	$21.60
7 purchase totals =	$777.79		$844.5217	$844.52	$844.55	$844.50