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	$120.29	6.538%	$128.1546	$128.15	$128.15	$128.20
Purchase #2	$10.33	12.436%	$11.6146	$11.61	$11.60	$11.60
Purchase #3	$51.33	12.596%	$57.7955	$57.80	$57.80	$57.80
Purchase #4	$26.36	9.818%	$28.948	$28.95	$28.95	$28.90
Purchase #5	$249.66	11.342%	$277.9764	$277.98	$278.00	$278.00
Purchase #6	$109.86	12.491%	$123.5826	$123.58	$123.60	$123.60
Purchase #7	$10.26	9.329%	$11.2172	$11.22	$11.20	$11.20
7 purchase totals =	$578.09		$639.2889	$639.29	$639.30	$639.30