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	$132.87	6.383%	$141.3511	$141.35	$141.35	$141.40
Purchase #2	$191.34	13.212%	$216.6198	$216.62	$216.60	$216.60
Purchase #3	$194.86	12.602%	$219.4163	$219.42	$219.40	$219.40
Purchase #4	$230.34	3.393%	$238.1554	$238.16	$238.15	$238.20
Purchase #5	$46.46	9.776%	$51.0019	$51.00	$51.00	$51.00
Purchase #6	$230.77	8.278%	$249.8731	$249.87	$249.85	$249.90
Purchase #7	$38.38	10.565%	$42.4348	$42.43	$42.45	$42.40
7 purchase totals =	$1,065.02		$1,158.8524	$1,158.85	$1,158.80	$1,158.90