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	$126.78	10.289%	$139.8244	$139.82	$139.80	$139.80
Purchase #2	$205.48	6.348%	$218.5239	$218.52	$218.50	$218.50
Purchase #3	$132.55	8.659%	$144.0275	$144.03	$144.05	$144.00
Purchase #4	$95.60	5.687%	$101.0368	$101.04	$101.05	$101.00
Purchase #5	$78.61	13.693%	$89.3741	$89.37	$89.35	$89.40
Purchase #6	$28.72	10.663%	$31.7824	$31.78	$31.80	$31.80
Purchase #7	$194.45	8.560%	$211.0949	$211.09	$211.10	$211.10
7 purchase totals =	$862.19		$935.6640	$935.65	$935.65	$935.60