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	$15.32	11.167%	$17.0308	$17.03	$17.05	$17.00
Purchase #2	$241.77	5.729%	$255.621	$255.62	$255.60	$255.60
Purchase #3	$156.27	6.234%	$166.0119	$166.01	$166.00	$166.00
Purchase #4	$109.50	6.169%	$116.2551	$116.26	$116.25	$116.30
Purchase #5	$127.81	8.865%	$139.1404	$139.14	$139.15	$139.10
Purchase #6	$107.85	9.690%	$118.3007	$118.30	$118.30	$118.30
Purchase #7	$116.80	11.710%	$130.4773	$130.48	$130.50	$130.50
7 purchase totals =	$875.32		$942.8372	$942.84	$942.85	$942.80