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	$137.92	3.510%	$142.761	$142.76	$142.75	$142.80
Purchase #2	$99.26	11.583%	$110.7573	$110.76	$110.75	$110.80
Purchase #3	$25.51	11.714%	$28.4982	$28.50	$28.50	$28.50
Purchase #4	$216.34	9.684%	$237.2904	$237.29	$237.30	$237.30
Purchase #5	$20.71	4.773%	$21.6985	$21.70	$21.70	$21.70
Purchase #6	$205.67	12.597%	$231.5782	$231.58	$231.60	$231.60
Purchase #7	$192.26	6.866%	$205.4606	$205.46	$205.45	$205.50
7 purchase totals =	$897.67		$978.0442	$978.05	$978.05	$978.20