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	$19.37	11.491%	$21.5958	$21.60	$21.60	$21.60
Purchase #2	$120.32	12.670%	$135.5645	$135.56	$135.55	$135.60
Purchase #3	$37.78	8.143%	$40.8564	$40.86	$40.85	$40.90
Purchase #4	$211.64	7.762%	$228.0675	$228.07	$228.05	$228.10
Purchase #5	$50.98	4.132%	$53.0865	$53.09	$53.10	$53.10
Purchase #6	$126.48	10.330%	$139.5454	$139.55	$139.55	$139.50
Purchase #7	$134.33	7.287%	$144.1186	$144.12	$144.10	$144.10
7 purchase totals =	$700.90		$762.8347	$762.85	$762.80	$762.90