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	$43.28	7.481%	$46.5178	$46.52	$46.50	$46.50
Purchase #2	$47.93	10.295%	$52.8644	$52.86	$52.85	$52.90
Purchase #3	$230.52	9.337%	$252.0437	$252.04	$252.05	$252.00
Purchase #4	$122.65	4.480%	$128.1447	$128.14	$128.15	$128.10
Purchase #5	$54.25	10.133%	$59.7472	$59.75	$59.75	$59.70
Purchase #6	$122.37	11.577%	$136.5368	$136.54	$136.55	$136.50
Purchase #7	$22.69	9.125%	$24.7605	$24.76	$24.75	$24.80
7 purchase totals =	$643.69		$700.6151	$700.61	$700.60	$700.50