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	$73.31	10.548%	$81.0427	$81.04	$81.05	$81.00
Purchase #2	$164.32	9.196%	$179.4309	$179.43	$179.45	$179.40
Purchase #3	$214.37	3.530%	$221.9373	$221.94	$221.95	$221.90
Purchase #4	$114.40	10.652%	$126.5859	$126.59	$126.60	$126.60
Purchase #5	$183.57	4.785%	$192.3538	$192.35	$192.35	$192.40
Purchase #6	$82.86	9.293%	$90.5602	$90.56	$90.55	$90.60
Purchase #7	$142.59	5.722%	$150.749	$150.75	$150.75	$150.70
7 purchase totals =	$975.42		$1,042.6598	$1,042.66	$1,042.70	$1,042.60