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	$79.85	13.375%	$90.5299	$90.53	$90.55	$90.50
Purchase #2	$215.80	9.326%	$235.9255	$235.93	$235.95	$235.90
Purchase #3	$45.25	12.381%	$50.8524	$50.85	$50.85	$50.90
Purchase #4	$117.95	7.492%	$126.7868	$126.79	$126.80	$126.80
Purchase #5	$133.42	3.862%	$138.5727	$138.57	$138.55	$138.60
Purchase #6	$84.49	6.522%	$90.0004	$90.00	$90.00	$90.00
Purchase #7	$152.45	10.607%	$168.6204	$168.62	$168.60	$168.60
7 purchase totals =	$829.21		$901.2881	$901.29	$901.30	$901.30