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	$8.30	10.177%	$9.1447	$9.14	$9.15	$9.10
Purchase #2	$55.78	12.219%	$62.5958	$62.60	$62.60	$62.60
Purchase #3	$169.90	6.444%	$180.8484	$180.85	$180.85	$180.80
Purchase #4	$100.55	11.307%	$111.9192	$111.92	$111.90	$111.90
Purchase #5	$89.52	12.295%	$100.5265	$100.53	$100.55	$100.50
Purchase #6	$221.60	9.532%	$242.7229	$242.72	$242.70	$242.70
Purchase #7	$129.37	6.497%	$137.7752	$137.78	$137.80	$137.80
7 purchase totals =	$775.02		$845.5327	$845.54	$845.55	$845.40