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	$74.44	12.363%	$83.643	$83.64	$83.65	$83.60
Purchase #2	$12.65	6.357%	$13.4542	$13.45	$13.45	$13.50
Purchase #3	$42.62	13.832%	$48.5152	$48.52	$48.50	$48.50
Purchase #4	$198.97	7.708%	$214.3066	$214.31	$214.30	$214.30
Purchase #5	$116.27	6.595%	$123.938	$123.94	$123.95	$123.90
Purchase #6	$200.45	7.793%	$216.0711	$216.07	$216.05	$216.10
Purchase #7	$135.51	8.187%	$146.6042	$146.60	$146.60	$146.60
7 purchase totals =	$780.91		$846.5323	$846.53	$846.50	$846.50