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	$60.32	11.828%	$67.4546	$67.45	$67.45	$67.50
Purchase #2	$208.68	6.707%	$222.6762	$222.68	$222.70	$222.70
Purchase #3	$224.68	13.861%	$255.8229	$255.82	$255.80	$255.80
Purchase #4	$95.93	3.205%	$99.0046	$99.00	$99.00	$99.00
Purchase #5	$99.61	6.265%	$105.8506	$105.85	$105.85	$105.90
Purchase #6	$181.60	9.462%	$198.783	$198.78	$198.80	$198.80
Purchase #7	$130.37	6.787%	$139.2182	$139.22	$139.20	$139.20
7 purchase totals =	$1,001.19		$1,088.8101	$1,088.80	$1,088.80	$1,088.90