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	$135.43	6.163%	$143.7766	$143.78	$143.80	$143.80
Purchase #2	$157.56	10.201%	$173.6327	$173.63	$173.65	$173.60
Purchase #3	$201.74	3.841%	$209.4888	$209.49	$209.50	$209.50
Purchase #4	$10.72	3.404%	$11.0849	$11.08	$11.10	$11.10
Purchase #5	$159.38	4.324%	$166.2716	$166.27	$166.25	$166.30
Purchase #6	$64.95	11.763%	$72.5901	$72.59	$72.60	$72.60
Purchase #7	$62.44	6.594%	$66.5573	$66.56	$66.55	$66.60
7 purchase totals =	$792.22		$843.4020	$843.40	$843.45	$843.50