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	$40.31	8.349%	$43.6755	$43.68	$43.70	$43.70
Purchase #2	$86.66	9.778%	$95.1336	$95.13	$95.15	$95.10
Purchase #3	$18.75	4.474%	$19.5889	$19.59	$19.60	$19.60
Purchase #4	$171.55	12.110%	$192.3247	$192.32	$192.30	$192.30
Purchase #5	$95.65	13.489%	$108.5522	$108.55	$108.55	$108.60
Purchase #6	$24.40	11.372%	$27.1748	$27.17	$27.15	$27.20
Purchase #7	$139.75	9.371%	$152.846	$152.85	$152.85	$152.80
7 purchase totals =	$577.07		$639.2957	$639.29	$639.30	$639.30