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	$67.90	7.698%	$73.1269	$73.13	$73.15	$73.10
Purchase #2	$182.64	12.700%	$205.8353	$205.84	$205.85	$205.80
Purchase #3	$20.56	4.560%	$21.4975	$21.50	$21.50	$21.50
Purchase #4	$200.68	4.866%	$210.4451	$210.45	$210.45	$210.40
Purchase #5	$143.93	7.414%	$154.601	$154.60	$154.60	$154.60
Purchase #6	$95.39	12.352%	$107.1726	$107.17	$107.15	$107.20
Purchase #7	$42.56	10.188%	$46.896	$46.90	$46.90	$46.90
7 purchase totals =	$753.66		$819.5744	$819.59	$819.60	$819.50