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	$72.42	7.753%	$78.0347	$78.03	$78.05	$78.00
Purchase #2	$141.53	7.297%	$151.8574	$151.86	$151.85	$151.90
Purchase #3	$45.79	3.436%	$47.3633	$47.36	$47.35	$47.40
Purchase #4	$172.86	9.752%	$189.7173	$189.72	$189.70	$189.70
Purchase #5	$12.39	13.699%	$14.0873	$14.09	$14.10	$14.10
Purchase #6	$20.70	3.540%	$21.4328	$21.43	$21.45	$21.40
Purchase #7	$164.56	12.857%	$185.7175	$185.72	$185.70	$185.70
7 purchase totals =	$630.25		$688.2103	$688.21	$688.20	$688.20