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	$138.95	11.135%	$154.4221	$154.42	$154.40	$154.40
Purchase #2	$160.25	9.644%	$175.7045	$175.70	$175.70	$175.70
Purchase #3	$14.32	8.731%	$15.5703	$15.57	$15.55	$15.60
Purchase #4	$143.79	10.152%	$158.3876	$158.39	$158.40	$158.40
Purchase #5	$100.71	10.766%	$111.5524	$111.55	$111.55	$111.60
Purchase #6	$242.71	12.853%	$273.9055	$273.91	$273.90	$273.90
Purchase #7	$38.81	9.657%	$42.5579	$42.56	$42.55	$42.60
7 purchase totals =	$839.54		$932.1003	$932.10	$932.05	$932.20