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	$58.44	13.192%	$66.1494	$66.15	$66.15	$66.10
Purchase #2	$195.25	7.104%	$209.1206	$209.12	$209.10	$209.10
Purchase #3	$133.44	8.218%	$144.4061	$144.41	$144.40	$144.40
Purchase #4	$140.60	8.397%	$152.4062	$152.41	$152.40	$152.40
Purchase #5	$70.29	10.308%	$77.5355	$77.54	$77.55	$77.50
Purchase #6	$183.28	3.657%	$189.9825	$189.98	$190.00	$190.00
Purchase #7	$167.82	5.384%	$176.8554	$176.86	$176.85	$176.90
7 purchase totals =	$949.12		$1,016.4557	$1,016.47	$1,016.45	$1,016.40