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	$27.45	9.518%	$30.0627	$30.06	$30.05	$30.10
Purchase #2	$38.89	3.237%	$40.1489	$40.15	$40.15	$40.10
Purchase #3	$101.87	9.780%	$111.8329	$111.83	$111.85	$111.80
Purchase #4	$44.52	5.194%	$46.8324	$46.83	$46.85	$46.80
Purchase #5	$186.98	4.841%	$196.0317	$196.03	$196.05	$196.00
Purchase #6	$219.81	9.365%	$240.3952	$240.40	$240.40	$240.40
Purchase #7	$134.31	8.859%	$146.2085	$146.21	$146.20	$146.20
7 purchase totals =	$753.83		$811.5123	$811.51	$811.55	$811.40