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	$225.27	13.493%	$255.6657	$255.67	$255.65	$255.70
Purchase #2	$128.29	12.596%	$144.4494	$144.45	$144.45	$144.40
Purchase #3	$29.52	10.352%	$32.5759	$32.58	$32.60	$32.60
Purchase #4	$239.65	4.203%	$249.7225	$249.72	$249.70	$249.70
Purchase #5	$164.55	9.158%	$179.6195	$179.62	$179.60	$179.60
Purchase #6	$76.29	7.193%	$81.7775	$81.78	$81.80	$81.80
Purchase #7	$154.35	13.289%	$174.8616	$174.86	$174.85	$174.90
7 purchase totals =	$1,017.92		$1,118.6721	$1,118.68	$1,118.65	$1,118.70