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	$249.78	11.654%	$278.8894	$278.89	$278.90	$278.90
Purchase #2	$188.78	9.790%	$207.2616	$207.26	$207.25	$207.30
Purchase #3	$33.32	10.720%	$36.8919	$36.89	$36.90	$36.90
Purchase #4	$79.48	10.326%	$87.6871	$87.69	$87.70	$87.70
Purchase #5	$99.27	5.748%	$104.976	$104.98	$105.00	$105.00
Purchase #6	$54.51	12.790%	$61.4818	$61.48	$61.50	$61.50
Purchase #7	$158.94	13.810%	$180.8896	$180.89	$180.90	$180.90
7 purchase totals =	$864.08		$958.0774	$958.08	$958.15	$958.20