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	$100.57	4.804%	$105.4014	$105.40	$105.40	$105.40
Purchase #2	$232.58	10.774%	$257.6382	$257.64	$257.65	$257.60
Purchase #3	$156.39	11.113%	$173.7696	$173.77	$173.75	$173.80
Purchase #4	$119.34	6.451%	$127.0386	$127.04	$127.05	$127.00
Purchase #5	$14.52	6.510%	$15.4653	$15.47	$15.45	$15.50
Purchase #6	$52.40	11.123%	$58.2285	$58.23	$58.25	$58.20
Purchase #7	$120.79	4.536%	$126.269	$126.27	$126.25	$126.30
7 purchase totals =	$796.59		$863.8106	$863.82	$863.80	$863.80