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	$51.72	7.332%	$55.5121	$55.51	$55.50	$55.50
Purchase #2	$60.50	3.493%	$62.6133	$62.61	$62.60	$62.60
Purchase #3	$131.39	9.125%	$143.3793	$143.38	$143.40	$143.40
Purchase #4	$80.65	12.694%	$90.8877	$90.89	$90.90	$90.90
Purchase #5	$148.91	9.304%	$162.7646	$162.76	$162.75	$162.80
Purchase #6	$54.39	5.599%	$57.4353	$57.44	$57.45	$57.40
Purchase #7	$54.93	9.368%	$60.0758	$60.08	$60.10	$60.10
7 purchase totals =	$582.49		$632.6681	$632.67	$632.70	$632.70