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	$166.54	10.545%	$184.1016	$184.10	$184.10	$184.10
Purchase #2	$118.96	4.661%	$124.5047	$124.50	$124.50	$124.50
Purchase #3	$92.89	7.747%	$100.0862	$100.09	$100.10	$100.10
Purchase #4	$116.43	13.583%	$132.2447	$132.24	$132.25	$132.20
Purchase #5	$117.52	9.208%	$128.3412	$128.34	$128.35	$128.30
Purchase #6	$164.87	3.384%	$170.4492	$170.45	$170.45	$170.40
Purchase #7	$120.35	6.699%	$128.4122	$128.41	$128.40	$128.40
7 purchase totals =	$897.56		$968.1398	$968.13	$968.15	$968.00