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	$20.49	10.321%	$22.6048	$22.60	$22.60	$22.60
Purchase #2	$202.79	12.185%	$227.5	$227.50	$227.50	$227.50
Purchase #3	$179.46	3.531%	$185.7967	$185.80	$185.80	$185.80
Purchase #4	$241.39	3.337%	$249.4452	$249.45	$249.45	$249.40
Purchase #5	$240.82	4.166%	$250.8526	$250.85	$250.85	$250.90
Purchase #6	$227.56	12.111%	$255.1198	$255.12	$255.10	$255.10
Purchase #7	$198.62	9.323%	$217.1373	$217.14	$217.15	$217.10
7 purchase totals =	$1,311.13		$1,408.4564	$1,408.46	$1,408.45	$1,408.40