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	$20.67	10.845%	$22.9117	$22.91	$22.90	$22.90
Purchase #2	$63.53	7.233%	$68.1251	$68.13	$68.15	$68.10
Purchase #3	$105.90	6.125%	$112.3864	$112.39	$112.40	$112.40
Purchase #4	$240.89	6.474%	$256.4852	$256.49	$256.50	$256.50
Purchase #5	$54.90	7.214%	$58.8605	$58.86	$58.85	$58.90
Purchase #6	$39.43	7.615%	$42.4326	$42.43	$42.45	$42.40
Purchase #7	$48.42	10.673%	$53.5879	$53.59	$53.60	$53.60
7 purchase totals =	$573.74		$614.7894	$614.80	$614.85	$614.80