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	$230.31	12.175%	$258.3502	$258.35	$258.35	$258.40
Purchase #2	$112.88	6.691%	$120.4328	$120.43	$120.45	$120.40
Purchase #3	$134.29	4.164%	$139.8818	$139.88	$139.90	$139.90
Purchase #4	$31.35	10.326%	$34.5872	$34.59	$34.60	$34.60
Purchase #5	$100.95	11.182%	$112.2382	$112.24	$112.25	$112.20
Purchase #6	$60.54	10.470%	$66.8785	$66.88	$66.90	$66.90
Purchase #7	$68.62	6.121%	$72.8202	$72.82	$72.80	$72.80
7 purchase totals =	$738.94		$805.1889	$805.19	$805.25	$805.20