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	$45.55	11.345%	$50.7176	$50.72	$50.70	$50.70
Purchase #2	$22.87	9.211%	$24.9766	$24.98	$25.00	$25.00
Purchase #3	$133.74	4.374%	$139.5898	$139.59	$139.60	$139.60
Purchase #4	$197.54	3.466%	$204.3867	$204.39	$204.40	$204.40
Purchase #5	$231.73	13.452%	$262.9023	$262.90	$262.90	$262.90
Purchase #6	$144.88	3.599%	$150.0942	$150.09	$150.10	$150.10
Purchase #7	$94.98	5.785%	$100.4746	$100.47	$100.45	$100.50
7 purchase totals =	$871.29		$933.1418	$933.14	$933.15	$933.20