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	$246.65	13.500%	$279.9478	$279.95	$279.95	$279.90
Purchase #2	$76.81	11.717%	$85.8098	$85.81	$85.80	$85.80
Purchase #3	$63.28	10.805%	$70.1174	$70.12	$70.10	$70.10
Purchase #4	$88.60	9.676%	$97.1729	$97.17	$97.15	$97.20
Purchase #5	$95.48	5.274%	$100.5156	$100.52	$100.50	$100.50
Purchase #6	$49.30	12.114%	$55.2722	$55.27	$55.25	$55.30
Purchase #7	$242.71	5.579%	$256.2508	$256.25	$256.25	$256.30
7 purchase totals =	$862.83		$945.0865	$945.09	$945.00	$945.10