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	$37.71	7.508%	$40.5413	$40.54	$40.55	$40.50
Purchase #2	$141.52	6.112%	$150.1697	$150.17	$150.15	$150.20
Purchase #3	$122.39	4.438%	$127.8217	$127.82	$127.80	$127.80
Purchase #4	$126.83	9.664%	$139.0869	$139.09	$139.10	$139.10
Purchase #5	$162.29	8.105%	$175.4436	$175.44	$175.45	$175.40
Purchase #6	$14.77	6.853%	$15.7822	$15.78	$15.80	$15.80
Purchase #7	$27.52	12.617%	$30.9922	$30.99	$31.00	$31.00
7 purchase totals =	$633.03		$679.8376	$679.83	$679.85	$679.80