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	$89.31	10.724%	$98.8876	$98.89	$98.90	$98.90
Purchase #2	$37.44	9.849%	$41.1275	$41.13	$41.15	$41.10
Purchase #3	$215.27	10.649%	$238.1941	$238.19	$238.20	$238.20
Purchase #4	$16.54	11.511%	$18.4439	$18.44	$18.45	$18.40
Purchase #5	$105.85	6.641%	$112.8795	$112.88	$112.90	$112.90
Purchase #6	$18.36	8.608%	$19.9404	$19.94	$19.95	$19.90
Purchase #7	$60.77	3.768%	$63.0598	$63.06	$63.05	$63.10
7 purchase totals =	$543.54		$592.5328	$592.53	$592.60	$592.50