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	$13.32	13.176%	$15.075	$15.08	$15.10	$15.10
Purchase #2	$63.65	13.674%	$72.3535	$72.35	$72.35	$72.40
Purchase #3	$177.63	12.747%	$200.2725	$200.27	$200.25	$200.30
Purchase #4	$224.54	13.599%	$255.0752	$255.08	$255.10	$255.10
Purchase #5	$157.83	11.779%	$176.4208	$176.42	$176.40	$176.40
Purchase #6	$76.36	9.658%	$83.7348	$83.73	$83.75	$83.70
Purchase #7	$198.90	8.822%	$216.447	$216.45	$216.45	$216.40
7 purchase totals =	$912.23		$1,019.3788	$1,019.38	$1,019.40	$1,019.40