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	$158.90	4.842%	$166.5939	$166.59	$166.60	$166.60
Purchase #2	$38.83	10.311%	$42.8338	$42.83	$42.85	$42.80
Purchase #3	$131.55	10.162%	$144.9181	$144.92	$144.90	$144.90
Purchase #4	$242.30	5.149%	$254.776	$254.78	$254.80	$254.80
Purchase #5	$58.77	8.553%	$63.7966	$63.80	$63.80	$63.80
Purchase #6	$77.91	8.346%	$84.4124	$84.41	$84.40	$84.40
Purchase #7	$6.30	3.230%	$6.5035	$6.50	$6.50	$6.50
7 purchase totals =	$714.56		$763.8343	$763.83	$763.85	$763.80