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	$29.55	13.700%	$33.5984	$33.60	$33.60	$33.60
Purchase #2	$58.96	3.561%	$61.0596	$61.06	$61.05	$61.10
Purchase #3	$92.86	12.553%	$104.5167	$104.52	$104.50	$104.50
Purchase #4	$98.80	12.522%	$111.1717	$111.17	$111.15	$111.20
Purchase #5	$234.43	10.136%	$258.1918	$258.19	$258.20	$258.20
Purchase #6	$213.30	3.548%	$220.8679	$220.87	$220.85	$220.90
Purchase #7	$89.69	11.606%	$100.0994	$100.10	$100.10	$100.10
7 purchase totals =	$817.59		$889.5055	$889.51	$889.45	$889.60