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	$244.65	13.204%	$276.9536	$276.95	$276.95	$277.00
Purchase #2	$41.77	11.542%	$46.5911	$46.59	$46.60	$46.60
Purchase #3	$219.30	3.789%	$227.6093	$227.61	$227.60	$227.60
Purchase #4	$77.40	4.778%	$81.0982	$81.10	$81.10	$81.10
Purchase #5	$79.70	12.669%	$89.7972	$89.80	$89.80	$89.80
Purchase #6	$117.82	5.115%	$123.8465	$123.85	$123.85	$123.80
Purchase #7	$37.66	3.822%	$39.0994	$39.10	$39.10	$39.10
7 purchase totals =	$818.30		$884.9953	$885.00	$885.00	$885.00