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	$72.60	11.424%	$80.8938	$80.89	$80.90	$80.90
Purchase #2	$53.95	8.156%	$58.3502	$58.35	$58.35	$58.40
Purchase #3	$101.37	3.798%	$105.22	$105.22	$105.20	$105.20
Purchase #4	$199.55	4.466%	$208.4619	$208.46	$208.45	$208.50
Purchase #5	$56.55	12.385%	$63.5537	$63.55	$63.55	$63.60
Purchase #6	$54.83	5.665%	$57.9361	$57.94	$57.95	$57.90
Purchase #7	$60.83	11.252%	$67.6746	$67.67	$67.65	$67.70
7 purchase totals =	$599.68		$642.0903	$642.08	$642.05	$642.20