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	$123.42	9.631%	$135.3066	$135.31	$135.30	$135.30
Purchase #2	$198.28	12.138%	$222.3472	$222.35	$222.35	$222.30
Purchase #3	$142.28	7.130%	$152.4246	$152.42	$152.40	$152.40
Purchase #4	$69.79	4.141%	$72.68	$72.68	$72.70	$72.70
Purchase #5	$100.88	13.298%	$114.295	$114.30	$114.30	$114.30
Purchase #6	$123.46	6.617%	$131.6293	$131.63	$131.65	$131.60
Purchase #7	$77.32	5.522%	$81.5896	$81.59	$81.60	$81.60
7 purchase totals =	$835.43		$910.2723	$910.28	$910.30	$910.20