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	$159.90	3.388%	$165.3174	$165.32	$165.30	$165.30
Purchase #2	$115.34	13.633%	$131.0643	$131.06	$131.05	$131.10
Purchase #3	$70.53	11.122%	$78.3743	$78.37	$78.35	$78.40
Purchase #4	$20.59	4.131%	$21.4406	$21.44	$21.45	$21.40
Purchase #5	$77.27	11.622%	$86.2503	$86.25	$86.25	$86.30
Purchase #6	$124.62	6.260%	$132.4212	$132.42	$132.40	$132.40
Purchase #7	$151.65	3.122%	$156.3845	$156.38	$156.40	$156.40
7 purchase totals =	$719.90		$771.2526	$771.24	$771.20	$771.30