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	$38.56	5.273%	$40.5933	$40.59	$40.60	$40.60
Purchase #2	$122.72	5.510%	$129.4819	$129.48	$129.50	$129.50
Purchase #3	$214.77	5.723%	$227.0613	$227.06	$227.05	$227.10
Purchase #4	$184.84	6.203%	$196.3056	$196.31	$196.30	$196.30
Purchase #5	$247.50	12.670%	$278.8583	$278.86	$278.85	$278.90
Purchase #6	$18.28	12.633%	$20.5893	$20.59	$20.60	$20.60
Purchase #7	$37.48	5.167%	$39.4166	$39.42	$39.40	$39.40
7 purchase totals =	$864.15		$932.3063	$932.31	$932.30	$932.40