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	$69.87	12.808%	$78.8189	$78.82	$78.80	$78.80
Purchase #2	$132.99	8.501%	$144.2955	$144.30	$144.30	$144.30
Purchase #3	$125.88	9.461%	$137.7895	$137.79	$137.80	$137.80
Purchase #4	$152.87	6.229%	$162.3923	$162.39	$162.40	$162.40
Purchase #5	$170.60	12.444%	$191.8295	$191.83	$191.85	$191.80
Purchase #6	$19.72	4.696%	$20.6461	$20.65	$20.65	$20.60
Purchase #7	$232.57	5.269%	$244.8241	$244.82	$244.80	$244.80
7 purchase totals =	$904.50		$980.5959	$980.60	$980.60	$980.50