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	$42.83	5.283%	$45.0927	$45.09	$45.10	$45.10
Purchase #2	$36.52	5.283%	$38.4494	$38.45	$38.45	$38.40
Purchase #3	$81.46	12.583%	$91.7101	$91.71	$91.70	$91.70
Purchase #4	$179.35	3.565%	$185.7438	$185.74	$185.75	$185.70
Purchase #5	$54.27	9.636%	$59.4995	$59.50	$59.50	$59.50
Purchase #6	$81.78	13.157%	$92.5398	$92.54	$92.55	$92.50
Purchase #7	$17.81	4.424%	$18.5979	$18.60	$18.60	$18.60
7 purchase totals =	$494.02		$531.6332	$531.63	$531.65	$531.50