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	$57.96	9.354%	$63.3816	$63.38	$63.40	$63.40
Purchase #2	$236.68	9.337%	$258.7788	$258.78	$258.80	$258.80
Purchase #3	$82.86	7.734%	$89.2684	$89.27	$89.25	$89.30
Purchase #4	$138.95	5.376%	$146.42	$146.42	$146.40	$146.40
Purchase #5	$62.72	5.108%	$65.9237	$65.92	$65.90	$65.90
Purchase #6	$112.65	5.491%	$118.8356	$118.84	$118.85	$118.80
Purchase #7	$78.72	12.483%	$88.5466	$88.55	$88.55	$88.50
7 purchase totals =	$770.54		$831.1547	$831.16	$831.15	$831.10