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	$88.86	11.778%	$99.3259	$99.33	$99.35	$99.30
Purchase #2	$248.42	6.614%	$264.8505	$264.85	$264.85	$264.90
Purchase #3	$145.77	13.768%	$165.8396	$165.84	$165.85	$165.80
Purchase #4	$44.78	10.767%	$49.6015	$49.60	$49.60	$49.60
Purchase #5	$101.51	11.290%	$112.9705	$112.97	$112.95	$113.00
Purchase #6	$241.88	6.610%	$257.8683	$257.87	$257.85	$257.90
Purchase #7	$17.85	9.341%	$19.5174	$19.52	$19.50	$19.50
7 purchase totals =	$889.07		$969.9737	$969.98	$969.95	$970.00