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	$40.45	5.252%	$42.5744	$42.57	$42.55	$42.60
Purchase #2	$101.64	9.297%	$111.0895	$111.09	$111.10	$111.10
Purchase #3	$216.60	11.458%	$241.418	$241.42	$241.40	$241.40
Purchase #4	$21.31	7.794%	$22.9709	$22.97	$22.95	$23.00
Purchase #5	$238.90	9.676%	$262.016	$262.02	$262.00	$262.00
Purchase #6	$65.25	9.464%	$71.4253	$71.43	$71.45	$71.40
Purchase #7	$225.83	5.839%	$239.0162	$239.02	$239.00	$239.00
7 purchase totals =	$909.98		$990.5103	$990.52	$990.45	$990.50