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	$26.81	10.408%	$29.6004	$29.60	$29.60	$29.60
Purchase #2	$104.80	11.200%	$116.5376	$116.54	$116.55	$116.50
Purchase #3	$145.83	10.612%	$161.3055	$161.31	$161.30	$161.30
Purchase #4	$217.45	6.338%	$231.232	$231.23	$231.25	$231.20
Purchase #5	$137.28	4.786%	$143.8502	$143.85	$143.85	$143.90
Purchase #6	$167.48	4.158%	$174.4438	$174.44	$174.45	$174.40
Purchase #7	$212.59	4.724%	$222.6328	$222.63	$222.65	$222.60
7 purchase totals =	$1,012.24		$1,079.6023	$1,079.60	$1,079.65	$1,079.50