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	$126.40	9.873%	$138.8795	$138.88	$138.90	$138.90
Purchase #2	$49.82	8.105%	$53.8579	$53.86	$53.85	$53.90
Purchase #3	$113.42	4.156%	$118.1337	$118.13	$118.15	$118.10
Purchase #4	$84.98	6.411%	$90.4281	$90.43	$90.45	$90.40
Purchase #5	$127.96	5.319%	$134.7662	$134.77	$134.75	$134.80
Purchase #6	$57.34	4.104%	$59.6932	$59.69	$59.70	$59.70
Purchase #7	$148.78	11.225%	$165.4806	$165.48	$165.50	$165.50
7 purchase totals =	$708.70		$761.2392	$761.24	$761.30	$761.30