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	$100.62	10.795%	$111.4819	$111.48	$111.50	$111.50
Purchase #2	$10.51	4.675%	$11.0013	$11.00	$11.00	$11.00
Purchase #3	$28.52	10.840%	$31.6116	$31.61	$31.60	$31.60
Purchase #4	$138.37	7.273%	$148.4337	$148.43	$148.45	$148.40
Purchase #5	$47.89	3.838%	$49.728	$49.73	$49.75	$49.70
Purchase #6	$15.43	5.425%	$16.2671	$16.27	$16.25	$16.30
Purchase #7	$38.82	9.154%	$42.3736	$42.37	$42.35	$42.40
7 purchase totals =	$380.16		$410.8972	$410.89	$410.90	$410.90