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	$42.81	6.458%	$45.5747	$45.57	$45.55	$45.60
Purchase #2	$80.52	12.522%	$90.6027	$90.60	$90.60	$90.60
Purchase #3	$13.93	9.513%	$15.2552	$15.26	$15.25	$15.30
Purchase #4	$224.56	13.631%	$255.1698	$255.17	$255.15	$255.20
Purchase #5	$172.70	7.336%	$185.3693	$185.37	$185.35	$185.40
Purchase #6	$32.38	4.616%	$33.8747	$33.87	$33.85	$33.90
Purchase #7	$134.81	10.352%	$148.7655	$148.77	$148.75	$148.80
7 purchase totals =	$701.71		$774.6119	$774.61	$774.50	$774.80