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	$11.44	7.837%	$12.3366	$12.34	$12.35	$12.30
Purchase #2	$179.79	4.157%	$187.2639	$187.26	$187.25	$187.30
Purchase #3	$123.52	7.357%	$132.6074	$132.61	$132.60	$132.60
Purchase #4	$209.48	3.799%	$217.4381	$217.44	$217.45	$217.40
Purchase #5	$70.42	11.301%	$78.3782	$78.38	$78.40	$78.40
Purchase #6	$225.53	13.466%	$255.8999	$255.90	$255.90	$255.90
Purchase #7	$76.63	11.463%	$85.4141	$85.41	$85.40	$85.40
7 purchase totals =	$896.81		$969.3382	$969.34	$969.35	$969.30