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	$41.90	6.845%	$44.7681	$44.77	$44.75	$44.80
Purchase #2	$235.61	7.440%	$253.1394	$253.14	$253.15	$253.10
Purchase #3	$229.47	11.396%	$255.6204	$255.62	$255.60	$255.60
Purchase #4	$86.96	4.274%	$90.6767	$90.68	$90.70	$90.70
Purchase #5	$80.66	6.869%	$86.2005	$86.20	$86.20	$86.20
Purchase #6	$36.40	4.469%	$38.0267	$38.03	$38.05	$38.00
Purchase #7	$108.92	7.258%	$116.8254	$116.83	$116.85	$116.80
7 purchase totals =	$819.92		$885.2572	$885.27	$885.30	$885.20