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	$250.37	6.746%	$267.26	$267.26	$267.25	$267.30
Purchase #2	$100.63	10.849%	$111.5473	$111.55	$111.55	$111.50
Purchase #3	$97.91	13.633%	$111.2581	$111.26	$111.25	$111.30
Purchase #4	$37.41	11.589%	$41.7454	$41.75	$41.75	$41.70
Purchase #5	$60.25	9.827%	$66.1708	$66.17	$66.15	$66.20
Purchase #6	$70.47	7.431%	$75.7066	$75.71	$75.70	$75.70
Purchase #7	$228.88	5.798%	$242.1505	$242.15	$242.15	$242.20
7 purchase totals =	$845.92		$915.8387	$915.85	$915.80	$915.90