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	$67.67	6.688%	$72.1958	$72.20	$72.20	$72.20
Purchase #2	$44.61	3.350%	$46.1044	$46.10	$46.10	$46.10
Purchase #3	$113.34	12.363%	$127.3522	$127.35	$127.35	$127.40
Purchase #4	$15.67	11.414%	$17.4586	$17.46	$17.45	$17.50
Purchase #5	$28.29	13.705%	$32.1671	$32.17	$32.15	$32.20
Purchase #6	$175.83	3.293%	$181.6201	$181.62	$181.60	$181.60
Purchase #7	$108.78	12.599%	$122.4852	$122.49	$122.50	$122.50
7 purchase totals =	$554.19		$599.3834	$599.39	$599.35	$599.50