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	$187.65	8.343%	$203.3056	$203.31	$203.30	$203.30
Purchase #2	$123.97	11.196%	$137.8497	$137.85	$137.85	$137.80
Purchase #3	$105.95	8.152%	$114.587	$114.59	$114.60	$114.60
Purchase #4	$120.75	9.829%	$132.6185	$132.62	$132.60	$132.60
Purchase #5	$20.67	9.468%	$22.627	$22.63	$22.65	$22.60
Purchase #6	$69.78	12.796%	$78.709	$78.71	$78.70	$78.70
Purchase #7	$127.86	9.119%	$139.5196	$139.52	$139.50	$139.50
7 purchase totals =	$756.63		$829.2164	$829.23	$829.20	$829.10