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	$151.83	13.809%	$172.7962	$172.80	$172.80	$172.80
Purchase #2	$129.85	8.297%	$140.6237	$140.62	$140.60	$140.60
Purchase #3	$121.29	4.576%	$126.8402	$126.84	$126.85	$126.80
Purchase #4	$153.44	10.405%	$169.4054	$169.41	$169.40	$169.40
Purchase #5	$240.65	6.274%	$255.7484	$255.75	$255.75	$255.70
Purchase #6	$170.78	8.739%	$185.7045	$185.70	$185.70	$185.70
Purchase #7	$29.93	5.404%	$31.5474	$31.55	$31.55	$31.50
7 purchase totals =	$997.77		$1,082.6658	$1,082.67	$1,082.65	$1,082.50