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	$92.26	13.439%	$104.6588	$104.66	$104.65	$104.70
Purchase #2	$137.84	6.376%	$146.6287	$146.63	$146.65	$146.60
Purchase #3	$53.27	8.751%	$57.9317	$57.93	$57.95	$57.90
Purchase #4	$127.95	3.718%	$132.7072	$132.71	$132.70	$132.70
Purchase #5	$74.82	7.612%	$80.5153	$80.52	$80.50	$80.50
Purchase #6	$80.45	12.308%	$90.3518	$90.35	$90.35	$90.40
Purchase #7	$150.86	7.395%	$162.0161	$162.02	$162.00	$162.00
7 purchase totals =	$717.45		$774.8096	$774.82	$774.80	$774.80