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	$8.71	10.690%	$9.6411	$9.64	$9.65	$9.60
Purchase #2	$216.42	12.749%	$244.0114	$244.01	$244.00	$244.00
Purchase #3	$139.88	9.112%	$152.6259	$152.63	$152.65	$152.60
Purchase #4	$230.33	5.207%	$242.3233	$242.32	$242.30	$242.30
Purchase #5	$19.61	11.423%	$21.8501	$21.85	$21.85	$21.90
Purchase #6	$166.63	10.477%	$184.0878	$184.09	$184.10	$184.10
Purchase #7	$111.70	10.874%	$123.8463	$123.85	$123.85	$123.80
7 purchase totals =	$893.28		$978.3859	$978.39	$978.40	$978.30