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	$244.91	4.242%	$255.2991	$255.30	$255.30	$255.30
Purchase #2	$249.56	13.794%	$283.9843	$283.98	$284.00	$284.00
Purchase #3	$21.84	11.397%	$24.3291	$24.33	$24.35	$24.30
Purchase #4	$33.62	13.838%	$38.2723	$38.27	$38.25	$38.30
Purchase #5	$117.28	11.820%	$131.1425	$131.14	$131.15	$131.10
Purchase #6	$136.39	13.262%	$154.478	$154.48	$154.50	$154.50
Purchase #7	$107.98	3.523%	$111.7841	$111.78	$111.80	$111.80
7 purchase totals =	$911.58		$999.2894	$999.28	$999.35	$999.30