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	$130.56	10.475%	$144.2362	$144.24	$144.25	$144.20
Purchase #2	$164.51	4.303%	$171.5889	$171.59	$171.60	$171.60
Purchase #3	$15.80	4.204%	$16.4642	$16.46	$16.45	$16.50
Purchase #4	$102.41	8.810%	$111.4323	$111.43	$111.45	$111.40
Purchase #5	$22.54	7.734%	$24.2832	$24.28	$24.30	$24.30
Purchase #6	$208.61	8.214%	$225.7452	$225.75	$225.75	$225.70
Purchase #7	$91.82	12.382%	$103.1892	$103.19	$103.20	$103.20
7 purchase totals =	$736.25		$796.9392	$796.94	$797.00	$796.90