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	$150.36	13.800%	$171.1097	$171.11	$171.10	$171.10
Purchase #2	$31.47	10.664%	$34.826	$34.83	$34.85	$34.80
Purchase #3	$79.80	4.536%	$83.4197	$83.42	$83.40	$83.40
Purchase #4	$150.52	11.779%	$168.2498	$168.25	$168.25	$168.20
Purchase #5	$40.64	3.200%	$41.9405	$41.94	$41.95	$41.90
Purchase #6	$72.49	3.388%	$74.946	$74.95	$74.95	$74.90
Purchase #7	$136.92	6.104%	$145.2776	$145.28	$145.30	$145.30
7 purchase totals =	$662.20		$719.7693	$719.78	$719.80	$719.60