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	$58.38	13.841%	$66.4604	$66.46	$66.45	$66.50
Purchase #2	$100.52	10.495%	$111.0696	$111.07	$111.05	$111.10
Purchase #3	$33.35	8.704%	$36.2528	$36.25	$36.25	$36.30
Purchase #4	$233.51	5.161%	$245.5615	$245.56	$245.55	$245.60
Purchase #5	$211.38	9.286%	$231.0087	$231.01	$231.00	$231.00
Purchase #6	$51.80	10.641%	$57.312	$57.31	$57.30	$57.30
Purchase #7	$92.42	13.705%	$105.0862	$105.09	$105.10	$105.10
7 purchase totals =	$781.36		$852.7512	$852.75	$852.70	$852.90