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	$86.90	4.387%	$90.7123	$90.71	$90.70	$90.70
Purchase #2	$205.32	12.286%	$230.5456	$230.55	$230.55	$230.50
Purchase #3	$222.32	10.709%	$246.1282	$246.13	$246.15	$246.10
Purchase #4	$46.51	4.170%	$48.4495	$48.45	$48.45	$48.40
Purchase #5	$71.65	8.678%	$77.8678	$77.87	$77.85	$77.90
Purchase #6	$65.53	10.674%	$72.5247	$72.52	$72.50	$72.50
Purchase #7	$90.53	13.727%	$102.9571	$102.96	$102.95	$103.00
7 purchase totals =	$788.76		$869.1852	$869.19	$869.15	$869.10