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	$34.70	11.252%	$38.6044	$38.60	$38.60	$38.60
Purchase #2	$38.69	6.334%	$41.1406	$41.14	$41.15	$41.10
Purchase #3	$127.53	13.553%	$144.8141	$144.81	$144.80	$144.80
Purchase #4	$99.29	12.130%	$111.3339	$111.33	$111.35	$111.30
Purchase #5	$164.39	11.310%	$182.9825	$182.98	$183.00	$183.00
Purchase #6	$226.30	3.478%	$234.1707	$234.17	$234.15	$234.20
Purchase #7	$24.55	5.352%	$25.8639	$25.86	$25.85	$25.90
7 purchase totals =	$715.45		$778.9101	$778.89	$778.90	$778.90