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	$129.75	10.573%	$143.4685	$143.47	$143.45	$143.50
Purchase #2	$52.70	12.778%	$59.434	$59.43	$59.45	$59.40
Purchase #3	$184.39	4.451%	$192.5972	$192.60	$192.60	$192.60
Purchase #4	$123.44	13.556%	$140.1735	$140.17	$140.15	$140.20
Purchase #5	$51.76	10.123%	$56.9997	$57.00	$57.00	$57.00
Purchase #6	$95.33	10.860%	$105.6828	$105.68	$105.70	$105.70
Purchase #7	$132.99	6.153%	$141.1729	$141.17	$141.15	$141.20
7 purchase totals =	$770.36		$839.5286	$839.52	$839.50	$839.60