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	$89.87	10.722%	$99.5059	$99.51	$99.50	$99.50
Purchase #2	$9.80	8.434%	$10.6265	$10.63	$10.65	$10.60
Purchase #3	$247.32	13.169%	$279.8896	$279.89	$279.90	$279.90
Purchase #4	$160.52	12.638%	$180.8065	$180.81	$180.80	$180.80
Purchase #5	$53.47	4.558%	$55.9072	$55.91	$55.90	$55.90
Purchase #6	$81.60	10.242%	$89.9575	$89.96	$89.95	$90.00
Purchase #7	$249.34	6.743%	$266.153	$266.15	$266.15	$266.20
7 purchase totals =	$891.92		$982.8462	$982.86	$982.85	$982.90