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	$28.52	4.720%	$29.8661	$29.87	$29.85	$29.90
Purchase #2	$128.80	3.105%	$132.7992	$132.80	$132.80	$132.80
Purchase #3	$228.49	8.712%	$248.396	$248.40	$248.40	$248.40
Purchase #4	$229.82	11.355%	$255.9161	$255.92	$255.90	$255.90
Purchase #5	$119.50	6.817%	$127.6463	$127.65	$127.65	$127.60
Purchase #6	$132.93	8.443%	$144.1533	$144.15	$144.15	$144.20
Purchase #7	$25.95	11.227%	$28.8634	$28.86	$28.85	$28.90
7 purchase totals =	$894.01		$967.6404	$967.65	$967.60	$967.70