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	$68.49	8.791%	$74.511	$74.51	$74.50	$74.50
Purchase #2	$142.78	6.352%	$151.8494	$151.85	$151.85	$151.80
Purchase #3	$171.55	5.796%	$181.493	$181.49	$181.50	$181.50
Purchase #4	$114.83	11.535%	$128.0756	$128.08	$128.10	$128.10
Purchase #5	$23.51	3.218%	$24.2666	$24.27	$24.25	$24.30
Purchase #6	$224.54	13.761%	$255.4389	$255.44	$255.45	$255.40
Purchase #7	$136.73	13.611%	$155.3403	$155.34	$155.35	$155.30
7 purchase totals =	$882.43		$970.9748	$970.98	$971.00	$970.90