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	$144.52	10.355%	$159.485	$159.49	$159.50	$159.50
Purchase #2	$27.32	8.784%	$29.7198	$29.72	$29.70	$29.70
Purchase #3	$139.99	5.795%	$148.1024	$148.10	$148.10	$148.10
Purchase #4	$130.76	11.143%	$145.3306	$145.33	$145.35	$145.30
Purchase #5	$104.60	4.347%	$109.147	$109.15	$109.15	$109.10
Purchase #6	$196.92	7.423%	$211.5374	$211.54	$211.55	$211.50
Purchase #7	$121.92	13.847%	$138.8023	$138.80	$138.80	$138.80
7 purchase totals =	$866.03		$942.1245	$942.13	$942.15	$942.00