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	$42.72	6.221%	$45.3776	$45.38	$45.40	$45.40
Purchase #2	$11.49	13.431%	$13.0332	$13.03	$13.05	$13.00
Purchase #3	$20.87	10.466%	$23.0543	$23.05	$23.05	$23.10
Purchase #4	$239.46	4.233%	$249.5963	$249.60	$249.60	$249.60
Purchase #5	$9.54	11.236%	$10.6119	$10.61	$10.60	$10.60
Purchase #6	$197.51	8.805%	$214.9008	$214.90	$214.90	$214.90
Purchase #7	$39.58	13.436%	$44.898	$44.90	$44.90	$44.90
7 purchase totals =	$561.17		$601.4721	$601.47	$601.50	$601.50