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	$158.36	12.646%	$178.3862	$178.39	$178.40	$178.40
Purchase #2	$134.25	13.290%	$152.0918	$152.09	$152.10	$152.10
Purchase #3	$112.63	13.298%	$127.6075	$127.61	$127.60	$127.60
Purchase #4	$178.80	4.648%	$187.1106	$187.11	$187.10	$187.10
Purchase #5	$151.30	8.380%	$163.9789	$163.98	$164.00	$164.00
Purchase #6	$134.78	3.405%	$139.3693	$139.37	$139.35	$139.40
Purchase #7	$126.90	9.311%	$138.7157	$138.72	$138.70	$138.70
7 purchase totals =	$997.02		$1,087.2600	$1,087.27	$1,087.25	$1,087.30