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	$116.91	5.128%	$122.9051	$122.91	$122.90	$122.90
Purchase #2	$139.77	8.760%	$152.0139	$152.01	$152.00	$152.00
Purchase #3	$137.38	9.468%	$150.3871	$150.39	$150.40	$150.40
Purchase #4	$104.47	6.659%	$111.4267	$111.43	$111.45	$111.40
Purchase #5	$124.71	5.713%	$131.8347	$131.83	$131.85	$131.80
Purchase #6	$11.54	13.603%	$13.1098	$13.11	$13.10	$13.10
Purchase #7	$127.80	13.239%	$144.7194	$144.72	$144.70	$144.70
7 purchase totals =	$762.58		$826.3967	$826.40	$826.40	$826.30