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	$92.55	8.589%	$100.4991	$100.50	$100.50	$100.50
Purchase #2	$89.87	11.826%	$100.498	$100.50	$100.50	$100.50
Purchase #3	$107.58	3.250%	$111.0764	$111.08	$111.10	$111.10
Purchase #4	$214.36	4.359%	$223.704	$223.70	$223.70	$223.70
Purchase #5	$34.66	9.866%	$38.0796	$38.08	$38.10	$38.10
Purchase #6	$93.81	13.676%	$106.6395	$106.64	$106.65	$106.60
Purchase #7	$139.81	9.301%	$152.8137	$152.81	$152.80	$152.80
7 purchase totals =	$772.64		$833.3103	$833.31	$833.35	$833.30