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	$11.73	11.863%	$13.1215	$13.12	$13.10	$13.10
Purchase #2	$203.71	13.817%	$231.8566	$231.86	$231.85	$231.90
Purchase #3	$58.50	12.134%	$65.5984	$65.60	$65.60	$65.60
Purchase #4	$97.89	13.453%	$111.0591	$111.06	$111.05	$111.10
Purchase #5	$167.39	12.110%	$187.6609	$187.66	$187.65	$187.70
Purchase #6	$42.29	12.172%	$47.4375	$47.44	$47.45	$47.40
Purchase #7	$60.43	10.540%	$66.7993	$66.80	$66.80	$66.80
7 purchase totals =	$641.94		$723.5333	$723.54	$723.50	$723.60