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	$51.95	5.536%	$54.826	$54.83	$54.85	$54.80
Purchase #2	$141.29	9.846%	$155.2014	$155.20	$155.20	$155.20
Purchase #3	$80.51	12.756%	$90.7799	$90.78	$90.80	$90.80
Purchase #4	$12.48	7.545%	$13.4216	$13.42	$13.40	$13.40
Purchase #5	$207.62	8.439%	$225.1411	$225.14	$225.15	$225.10
Purchase #6	$85.33	5.631%	$90.1349	$90.13	$90.15	$90.10
Purchase #7	$103.48	12.364%	$116.2743	$116.27	$116.25	$116.30
7 purchase totals =	$682.66		$745.7792	$745.77	$745.80	$745.70