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	$207.63	6.148%	$220.3951	$220.40	$220.40	$220.40
Purchase #2	$238.60	7.169%	$255.7052	$255.71	$255.70	$255.70
Purchase #3	$163.51	9.134%	$178.445	$178.45	$178.45	$178.40
Purchase #4	$134.45	11.772%	$150.2775	$150.28	$150.30	$150.30
Purchase #5	$102.37	8.793%	$111.3714	$111.37	$111.35	$111.40
Purchase #6	$208.72	6.770%	$222.8503	$222.85	$222.85	$222.90
Purchase #7	$225.48	13.263%	$255.3854	$255.39	$255.40	$255.40
7 purchase totals =	$1,280.76		$1,394.4299	$1,394.45	$1,394.45	$1,394.50