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	$38.98	8.687%	$42.3662	$42.37	$42.35	$42.40
Purchase #2	$51.29	7.836%	$55.3091	$55.31	$55.30	$55.30
Purchase #3	$121.27	4.790%	$127.0788	$127.08	$127.10	$127.10
Purchase #4	$63.96	13.336%	$72.4897	$72.49	$72.50	$72.50
Purchase #5	$77.96	3.559%	$80.7346	$80.73	$80.75	$80.70
Purchase #6	$146.95	8.103%	$158.8574	$158.86	$158.85	$158.90
Purchase #7	$24.60	10.866%	$27.273	$27.27	$27.25	$27.30
7 purchase totals =	$525.01		$564.1088	$564.11	$564.10	$564.20