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	$227.45	12.358%	$255.5583	$255.56	$255.55	$255.60
Purchase #2	$80.48	10.594%	$89.0061	$89.01	$89.00	$89.00
Purchase #3	$27.27	8.573%	$29.6079	$29.61	$29.60	$29.60
Purchase #4	$17.82	12.570%	$20.06	$20.06	$20.05	$20.10
Purchase #5	$67.98	9.270%	$74.2817	$74.28	$74.30	$74.30
Purchase #6	$13.70	13.658%	$15.5711	$15.57	$15.55	$15.60
Purchase #7	$32.26	4.400%	$33.6794	$33.68	$33.70	$33.70
7 purchase totals =	$466.96		$517.7645	$517.77	$517.75	$517.90