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	$19.40	10.746%	$21.4847	$21.48	$21.50	$21.50
Purchase #2	$30.64	13.589%	$34.8037	$34.80	$34.80	$34.80
Purchase #3	$162.59	9.615%	$178.223	$178.22	$178.20	$178.20
Purchase #4	$136.50	6.852%	$145.853	$145.85	$145.85	$145.90
Purchase #5	$42.50	7.211%	$45.5647	$45.56	$45.55	$45.60
Purchase #6	$205.93	13.185%	$233.0819	$233.08	$233.10	$233.10
Purchase #7	$48.81	3.567%	$50.5511	$50.55	$50.55	$50.60
7 purchase totals =	$646.37		$709.5621	$709.54	$709.55	$709.70