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	$82.92	9.479%	$90.78	$90.78	$90.80	$90.80
Purchase #2	$132.65	13.275%	$150.2593	$150.26	$150.25	$150.30
Purchase #3	$214.62	5.571%	$226.5765	$226.58	$226.60	$226.60
Purchase #4	$96.77	7.868%	$104.3839	$104.38	$104.40	$104.40
Purchase #5	$24.61	12.102%	$27.5883	$27.59	$27.60	$27.60
Purchase #6	$11.42	9.675%	$12.5249	$12.52	$12.50	$12.50
Purchase #7	$46.41	4.690%	$48.5866	$48.59	$48.60	$48.60
7 purchase totals =	$609.40		$660.6995	$660.70	$660.75	$660.80