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	$138.33	12.476%	$155.5881	$155.59	$155.60	$155.60
Purchase #2	$111.36	6.288%	$118.3623	$118.36	$118.35	$118.40
Purchase #3	$112.31	11.409%	$125.1234	$125.12	$125.10	$125.10
Purchase #4	$107.31	3.786%	$111.3728	$111.37	$111.35	$111.40
Purchase #5	$207.37	3.562%	$214.7565	$214.76	$214.75	$214.80
Purchase #6	$69.86	4.211%	$72.8018	$72.80	$72.80	$72.80
Purchase #7	$102.37	11.402%	$114.0422	$114.04	$114.05	$114.00
7 purchase totals =	$848.91		$912.0471	$912.04	$912.00	$912.10