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	$63.88	3.817%	$66.3183	$66.32	$66.30	$66.30
Purchase #2	$153.52	10.481%	$169.6104	$169.61	$169.60	$169.60
Purchase #3	$45.47	12.487%	$51.1478	$51.15	$51.15	$51.10
Purchase #4	$204.72	10.151%	$225.5011	$225.50	$225.50	$225.50
Purchase #5	$159.93	3.565%	$165.6315	$165.63	$165.65	$165.60
Purchase #6	$60.92	3.858%	$63.2703	$63.27	$63.25	$63.30
Purchase #7	$192.75	4.130%	$200.7106	$200.71	$200.70	$200.70
7 purchase totals =	$881.19		$942.1900	$942.19	$942.15	$942.10