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	$46.96	9.174%	$51.2681	$51.27	$51.25	$51.30
Purchase #2	$146.53	12.513%	$164.8653	$164.87	$164.85	$164.90
Purchase #3	$73.99	13.303%	$83.8329	$83.83	$83.85	$83.80
Purchase #4	$234.56	9.822%	$257.5985	$257.60	$257.60	$257.60
Purchase #5	$51.55	9.870%	$56.638	$56.64	$56.65	$56.60
Purchase #6	$99.45	3.717%	$103.1466	$103.15	$103.15	$103.10
Purchase #7	$54.77	13.567%	$62.2006	$62.20	$62.20	$62.20
7 purchase totals =	$707.81		$779.5500	$779.56	$779.55	$779.50