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	$169.46	6.565%	$180.585	$180.59	$180.60	$180.60
Purchase #2	$59.82	4.169%	$62.3139	$62.31	$62.30	$62.30
Purchase #3	$160.40	7.862%	$173.0106	$173.01	$173.00	$173.00
Purchase #4	$155.51	3.517%	$160.9793	$160.98	$161.00	$161.00
Purchase #5	$95.83	10.584%	$105.9726	$105.97	$105.95	$106.00
Purchase #6	$242.89	5.314%	$255.7972	$255.80	$255.80	$255.80
Purchase #7	$143.59	4.569%	$150.1506	$150.15	$150.15	$150.20
7 purchase totals =	$1,027.50		$1,088.8092	$1,088.81	$1,088.80	$1,088.90