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	$128.63	8.267%	$139.2638	$139.26	$139.25	$139.30
Purchase #2	$128.94	7.488%	$138.595	$138.60	$138.60	$138.60
Purchase #3	$138.74	11.269%	$154.3746	$154.37	$154.35	$154.40
Purchase #4	$59.72	9.710%	$65.5188	$65.52	$65.50	$65.50
Purchase #5	$76.59	3.473%	$79.25	$79.25	$79.25	$79.30
Purchase #6	$108.57	4.599%	$113.5631	$113.56	$113.55	$113.60
Purchase #7	$103.55	4.839%	$108.5608	$108.56	$108.55	$108.60
7 purchase totals =	$744.74		$799.1261	$799.12	$799.05	$799.30