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	$94.73	6.194%	$100.5976	$100.60	$100.60	$100.60
Purchase #2	$96.37	4.186%	$100.404	$100.40	$100.40	$100.40
Purchase #3	$142.98	5.397%	$150.6966	$150.70	$150.70	$150.70
Purchase #4	$14.78	4.557%	$15.4535	$15.45	$15.45	$15.50
Purchase #5	$133.52	7.401%	$143.4018	$143.40	$143.40	$143.40
Purchase #6	$100.61	3.181%	$103.8104	$103.81	$103.80	$103.80
Purchase #7	$110.65	10.349%	$122.1012	$122.10	$122.10	$122.10
7 purchase totals =	$693.64		$736.4651	$736.46	$736.45	$736.50