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	$56.71	8.539%	$61.5525	$61.55	$61.55	$61.60
Purchase #2	$73.25	9.564%	$80.2556	$80.26	$80.25	$80.30
Purchase #3	$214.96	10.752%	$238.0725	$238.07	$238.05	$238.10
Purchase #4	$46.49	13.248%	$52.649	$52.65	$52.65	$52.60
Purchase #5	$22.48	6.481%	$23.9369	$23.94	$23.95	$23.90
Purchase #6	$18.79	12.816%	$21.1981	$21.20	$21.20	$21.20
Purchase #7	$185.59	5.698%	$196.1649	$196.16	$196.15	$196.20
7 purchase totals =	$618.27		$673.8295	$673.83	$673.80	$673.90