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	$101.99	9.544%	$111.7239	$111.72	$111.70	$111.70
Purchase #2	$102.83	8.196%	$111.2579	$111.26	$111.25	$111.30
Purchase #3	$28.32	10.401%	$31.2656	$31.27	$31.25	$31.30
Purchase #4	$150.26	12.703%	$169.3475	$169.35	$169.35	$169.30
Purchase #5	$75.77	12.831%	$85.492	$85.49	$85.50	$85.50
Purchase #6	$19.30	12.549%	$21.722	$21.72	$21.70	$21.70
Purchase #7	$99.41	8.837%	$108.1949	$108.19	$108.20	$108.20
7 purchase totals =	$577.88		$639.0038	$639.00	$638.95	$639.00