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	$153.91	8.852%	$167.5341	$167.53	$167.55	$167.50
Purchase #2	$216.83	13.602%	$246.3232	$246.32	$246.30	$246.30
Purchase #3	$65.39	11.287%	$72.7706	$72.77	$72.75	$72.80
Purchase #4	$228.64	11.494%	$254.9199	$254.92	$254.90	$254.90
Purchase #5	$161.50	4.542%	$168.8353	$168.84	$168.85	$168.80
Purchase #6	$248.84	12.516%	$279.9848	$279.98	$280.00	$280.00
Purchase #7	$136.60	7.557%	$146.9229	$146.92	$146.90	$146.90
7 purchase totals =	$1,211.71		$1,337.2908	$1,337.28	$1,337.25	$1,337.20