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	$107.56	11.522%	$119.9531	$119.95	$119.95	$120.00
Purchase #2	$85.78	3.180%	$88.5078	$88.51	$88.50	$88.50
Purchase #3	$103.93	4.206%	$108.3013	$108.30	$108.30	$108.30
Purchase #4	$39.52	13.235%	$44.7505	$44.75	$44.75	$44.80
Purchase #5	$113.78	4.476%	$118.8728	$118.87	$118.85	$118.90
Purchase #6	$102.67	5.479%	$108.2953	$108.30	$108.30	$108.30
Purchase #7	$19.82	6.479%	$21.1041	$21.10	$21.10	$21.10
7 purchase totals =	$573.06		$609.7849	$609.78	$609.75	$609.90