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	$205.75	8.257%	$222.7388	$222.74	$222.75	$222.70
Purchase #2	$133.82	8.124%	$144.6915	$144.69	$144.70	$144.70
Purchase #3	$37.96	6.723%	$40.5121	$40.51	$40.50	$40.50
Purchase #4	$19.34	10.167%	$21.3063	$21.31	$21.30	$21.30
Purchase #5	$23.77	7.249%	$25.4931	$25.49	$25.50	$25.50
Purchase #6	$9.64	6.132%	$10.2311	$10.23	$10.25	$10.20
Purchase #7	$123.34	11.163%	$137.1084	$137.11	$137.10	$137.10
7 purchase totals =	$553.62		$602.0813	$602.08	$602.10	$602.00