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	$51.25	11.330%	$57.0566	$57.06	$57.05	$57.10
Purchase #2	$62.45	4.864%	$65.4876	$65.49	$65.50	$65.50
Purchase #3	$28.78	9.705%	$31.5731	$31.57	$31.55	$31.60
Purchase #4	$239.35	11.247%	$266.2697	$266.27	$266.25	$266.30
Purchase #5	$127.41	11.381%	$141.9105	$141.91	$141.90	$141.90
Purchase #6	$54.99	7.716%	$59.233	$59.23	$59.25	$59.20
Purchase #7	$52.74	9.450%	$57.7239	$57.72	$57.70	$57.70
7 purchase totals =	$616.97		$679.2544	$679.25	$679.20	$679.30