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	$37.62	4.501%	$39.3133	$39.31	$39.30	$39.30
Purchase #2	$192.76	11.642%	$215.2011	$215.20	$215.20	$215.20
Purchase #3	$151.95	6.429%	$161.7189	$161.72	$161.70	$161.70
Purchase #4	$239.64	10.662%	$265.1904	$265.19	$265.20	$265.20
Purchase #5	$134.89	7.314%	$144.7559	$144.76	$144.75	$144.80
Purchase #6	$76.38	12.140%	$85.6525	$85.65	$85.65	$85.70
Purchase #7	$27.72	13.545%	$31.4747	$31.47	$31.45	$31.50
7 purchase totals =	$860.96		$943.3068	$943.30	$943.25	$943.40