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	$45.55	12.233%	$51.1221	$51.12	$51.10	$51.10
Purchase #2	$148.67	9.852%	$163.317	$163.32	$163.30	$163.30
Purchase #3	$99.78	11.796%	$111.55	$111.55	$111.55	$111.60
Purchase #4	$81.65	12.181%	$91.5958	$91.60	$91.60	$91.60
Purchase #5	$100.56	6.847%	$107.4453	$107.45	$107.45	$107.40
Purchase #6	$126.44	3.712%	$131.1335	$131.13	$131.15	$131.10
Purchase #7	$185.75	7.606%	$199.8781	$199.88	$199.90	$199.90
7 purchase totals =	$788.40		$856.0418	$856.05	$856.05	$856.00