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	$6.50	11.665%	$7.2582	$7.26	$7.25	$7.30
Purchase #2	$139.79	9.453%	$153.0043	$153.00	$153.00	$153.00
Purchase #3	$18.60	13.136%	$21.0433	$21.04	$21.05	$21.00
Purchase #4	$133.77	6.716%	$142.754	$142.75	$142.75	$142.80
Purchase #5	$104.50	6.825%	$111.6321	$111.63	$111.65	$111.60
Purchase #6	$209.79	6.250%	$222.9019	$222.90	$222.90	$222.90
Purchase #7	$19.45	10.448%	$21.4821	$21.48	$21.50	$21.50
7 purchase totals =	$632.40		$680.0759	$680.06	$680.10	$680.10