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	$249.66	12.694%	$281.3518	$281.35	$281.35	$281.40
Purchase #2	$156.98	9.724%	$172.2447	$172.24	$172.25	$172.20
Purchase #3	$175.93	6.340%	$187.084	$187.08	$187.10	$187.10
Purchase #4	$175.92	8.307%	$190.5337	$190.53	$190.55	$190.50
Purchase #5	$132.54	6.534%	$141.2002	$141.20	$141.20	$141.20
Purchase #6	$98.82	4.706%	$103.4705	$103.47	$103.45	$103.50
Purchase #7	$60.52	4.468%	$63.224	$63.22	$63.20	$63.20
7 purchase totals =	$1,050.37		$1,139.1089	$1,139.09	$1,139.10	$1,139.10