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	$51.56	9.699%	$56.5608	$56.56	$56.55	$56.60
Purchase #2	$43.78	3.593%	$45.353	$45.35	$45.35	$45.40
Purchase #3	$131.90	5.205%	$138.7654	$138.77	$138.75	$138.80
Purchase #4	$10.52	4.275%	$10.9697	$10.97	$10.95	$11.00
Purchase #5	$49.54	6.441%	$52.7309	$52.73	$52.75	$52.70
Purchase #6	$165.45	8.510%	$179.5298	$179.53	$179.55	$179.50
Purchase #7	$126.72	11.374%	$141.1331	$141.13	$141.15	$141.10
7 purchase totals =	$579.47		$625.0427	$625.04	$625.05	$625.10