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	$53.38	11.472%	$59.5038	$59.50	$59.50	$59.50
Purchase #2	$131.26	5.774%	$138.839	$138.84	$138.85	$138.80
Purchase #3	$23.65	9.293%	$25.8478	$25.85	$25.85	$25.80
Purchase #4	$114.84	10.660%	$127.0819	$127.08	$127.10	$127.10
Purchase #5	$24.31	11.595%	$27.1287	$27.13	$27.15	$27.10
Purchase #6	$35.87	6.599%	$38.2371	$38.24	$38.25	$38.20
Purchase #7	$17.86	12.801%	$20.1463	$20.15	$20.15	$20.10
7 purchase totals =	$401.17		$436.7846	$436.79	$436.85	$436.60