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	$81.94	6.656%	$87.3939	$87.39	$87.40	$87.40
Purchase #2	$80.48	6.628%	$85.8142	$85.81	$85.80	$85.80
Purchase #3	$150.41	7.273%	$161.3493	$161.35	$161.35	$161.30
Purchase #4	$63.54	10.133%	$69.9785	$69.98	$70.00	$70.00
Purchase #5	$11.51	9.727%	$12.6296	$12.63	$12.65	$12.60
Purchase #6	$81.93	10.870%	$90.8358	$90.84	$90.85	$90.80
Purchase #7	$132.62	7.528%	$142.6036	$142.60	$142.60	$142.60
7 purchase totals =	$602.43		$650.6049	$650.60	$650.65	$650.50