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	$9.44	11.379%	$10.5142	$10.51	$10.50	$10.50
Purchase #2	$106.33	3.327%	$109.8676	$109.87	$109.85	$109.90
Purchase #3	$78.90	8.189%	$85.3611	$85.36	$85.35	$85.40
Purchase #4	$133.38	7.469%	$143.3422	$143.34	$143.35	$143.30
Purchase #5	$60.82	9.775%	$66.7652	$66.77	$66.75	$66.80
Purchase #6	$76.51	11.467%	$85.2834	$85.28	$85.30	$85.30
Purchase #7	$195.96	5.105%	$205.9638	$205.96	$205.95	$206.00
7 purchase totals =	$661.34		$707.0975	$707.09	$707.05	$707.20