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	$131.94	8.852%	$143.6193	$143.62	$143.60	$143.60
Purchase #2	$37.50	4.608%	$39.228	$39.23	$39.25	$39.20
Purchase #3	$77.25	6.688%	$82.4165	$82.42	$82.40	$82.40
Purchase #4	$51.71	10.283%	$57.0273	$57.03	$57.05	$57.00
Purchase #5	$192.70	12.734%	$217.2384	$217.24	$217.25	$217.20
Purchase #6	$55.34	13.527%	$62.8258	$62.83	$62.85	$62.80
Purchase #7	$52.89	11.775%	$59.1178	$59.12	$59.10	$59.10
7 purchase totals =	$599.33		$661.4731	$661.49	$661.50	$661.30