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	$178.75	12.184%	$200.5289	$200.53	$200.55	$200.50
Purchase #2	$123.66	13.521%	$140.3801	$140.38	$140.40	$140.40
Purchase #3	$12.52	3.749%	$12.9894	$12.99	$13.00	$13.00
Purchase #4	$241.29	8.786%	$262.4897	$262.49	$262.50	$262.50
Purchase #5	$196.51	9.774%	$215.7169	$215.72	$215.70	$215.70
Purchase #6	$133.65	6.662%	$142.5538	$142.55	$142.55	$142.60
Purchase #7	$163.82	11.579%	$182.7887	$182.79	$182.80	$182.80
7 purchase totals =	$1,050.20		$1,157.4475	$1,157.45	$1,157.50	$1,157.50