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	$61.83	7.737%	$66.6138	$66.61	$66.60	$66.60
Purchase #2	$172.51	4.529%	$180.323	$180.32	$180.30	$180.30
Purchase #3	$103.37	8.167%	$111.8122	$111.81	$111.80	$111.80
Purchase #4	$237.33	4.193%	$247.2812	$247.28	$247.30	$247.30
Purchase #5	$60.98	4.576%	$63.7704	$63.77	$63.75	$63.80
Purchase #6	$154.39	12.606%	$173.8524	$173.85	$173.85	$173.90
Purchase #7	$116.35	11.802%	$130.0816	$130.08	$130.10	$130.10
7 purchase totals =	$906.76		$973.7346	$973.72	$973.70	$973.80