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	$132.38	13.474%	$150.2169	$150.22	$150.20	$150.20
Purchase #2	$7.35	8.342%	$7.9631	$7.96	$7.95	$8.00
Purchase #3	$19.25	11.690%	$21.5003	$21.50	$21.50	$21.50
Purchase #4	$140.43	3.692%	$145.6147	$145.61	$145.60	$145.60
Purchase #5	$231.31	10.146%	$254.7787	$254.78	$254.80	$254.80
Purchase #6	$85.93	5.666%	$90.7988	$90.80	$90.80	$90.80
Purchase #7	$43.98	10.746%	$48.7061	$48.71	$48.70	$48.70
7 purchase totals =	$660.63		$719.5786	$719.58	$719.55	$719.60