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	$91.34	9.643%	$100.1479	$100.15	$100.15	$100.10
Purchase #2	$118.67	6.834%	$126.7799	$126.78	$126.80	$126.80
Purchase #3	$54.52	12.461%	$61.3137	$61.31	$61.30	$61.30
Purchase #4	$194.84	11.466%	$217.1804	$217.18	$217.20	$217.20
Purchase #5	$22.32	9.403%	$24.4187	$24.42	$24.40	$24.40
Purchase #6	$42.31	4.793%	$44.3379	$44.34	$44.35	$44.30
Purchase #7	$59.77	3.126%	$61.6384	$61.64	$61.65	$61.60
7 purchase totals =	$583.77		$635.8169	$635.82	$635.85	$635.70