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	$60.87	13.481%	$69.0759	$69.08	$69.10	$69.10
Purchase #2	$124.72	6.440%	$132.752	$132.75	$132.75	$132.80
Purchase #3	$105.64	5.641%	$111.5992	$111.60	$111.60	$111.60
Purchase #4	$65.72	8.449%	$71.2727	$71.27	$71.25	$71.30
Purchase #5	$63.94	12.128%	$71.6946	$71.69	$71.70	$71.70
Purchase #6	$166.82	3.361%	$172.4268	$172.43	$172.45	$172.40
Purchase #7	$78.55	3.450%	$81.26	$81.26	$81.25	$81.30
7 purchase totals =	$666.26		$710.0812	$710.08	$710.10	$710.20