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	$38.42	10.248%	$42.3573	$42.36	$42.35	$42.40
Purchase #2	$50.54	8.464%	$54.8177	$54.82	$54.80	$54.80
Purchase #3	$182.75	12.667%	$205.8989	$205.90	$205.90	$205.90
Purchase #4	$127.66	10.661%	$141.2698	$141.27	$141.25	$141.30
Purchase #5	$198.58	8.206%	$214.8755	$214.88	$214.90	$214.90
Purchase #6	$92.29	4.298%	$96.2566	$96.26	$96.25	$96.30
Purchase #7	$42.99	10.407%	$47.464	$47.46	$47.45	$47.50
7 purchase totals =	$733.23		$802.9398	$802.95	$802.90	$803.10