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	$181.35	13.119%	$205.1413	$205.14	$205.15	$205.10
Purchase #2	$56.40	11.444%	$62.8544	$62.85	$62.85	$62.90
Purchase #3	$189.83	12.419%	$213.405	$213.41	$213.40	$213.40
Purchase #4	$103.26	5.344%	$108.7782	$108.78	$108.80	$108.80
Purchase #5	$132.36	9.866%	$145.4186	$145.42	$145.40	$145.40
Purchase #6	$54.76	12.262%	$61.4747	$61.47	$61.45	$61.50
Purchase #7	$126.28	10.718%	$139.8147	$139.81	$139.80	$139.80
7 purchase totals =	$844.24		$936.8869	$936.88	$936.85	$936.90