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	$35.81	11.769%	$40.0245	$40.02	$40.00	$40.00
Purchase #2	$237.83	3.195%	$245.4287	$245.43	$245.45	$245.40
Purchase #3	$53.85	9.836%	$59.1467	$59.15	$59.15	$59.10
Purchase #4	$24.92	11.838%	$27.87	$27.87	$27.85	$27.90
Purchase #5	$154.97	8.425%	$168.0262	$168.03	$168.05	$168.00
Purchase #6	$25.55	7.303%	$27.4159	$27.42	$27.40	$27.40
Purchase #7	$223.94	13.740%	$254.7094	$254.71	$254.70	$254.70
7 purchase totals =	$756.87		$822.6214	$822.63	$822.60	$822.50