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	$29.32	8.164%	$31.7137	$31.71	$31.70	$31.70
Purchase #2	$48.47	4.853%	$50.8222	$50.82	$50.80	$50.80
Purchase #3	$250.81	12.247%	$281.5267	$281.53	$281.55	$281.50
Purchase #4	$69.93	12.729%	$78.8314	$78.83	$78.85	$78.80
Purchase #5	$192.96	11.852%	$215.8296	$215.83	$215.85	$215.80
Purchase #6	$220.96	4.131%	$230.0879	$230.09	$230.10	$230.10
Purchase #7	$204.26	5.778%	$216.0621	$216.06	$216.05	$216.10
7 purchase totals =	$1,016.71		$1,104.8736	$1,104.87	$1,104.90	$1,104.80