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	$46.51	9.462%	$50.9108	$50.91	$50.90	$50.90
Purchase #2	$72.68	13.471%	$82.4707	$82.47	$82.45	$82.50
Purchase #3	$98.48	13.506%	$111.7807	$111.78	$111.80	$111.80
Purchase #4	$59.69	11.309%	$66.4403	$66.44	$66.45	$66.40
Purchase #5	$183.67	9.491%	$201.1021	$201.10	$201.10	$201.10
Purchase #6	$21.56	11.268%	$23.9894	$23.99	$24.00	$24.00
Purchase #7	$39.40	6.139%	$41.8188	$41.82	$41.80	$41.80
7 purchase totals =	$521.99		$578.5128	$578.51	$578.50	$578.50