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	$37.70	5.602%	$39.812	$39.81	$39.80	$39.80
Purchase #2	$65.64	12.691%	$73.9704	$73.97	$73.95	$74.00
Purchase #3	$87.83	7.328%	$94.2662	$94.27	$94.25	$94.30
Purchase #4	$129.27	10.323%	$142.6145	$142.61	$142.60	$142.60
Purchase #5	$77.30	11.157%	$85.9244	$85.92	$85.90	$85.90
Purchase #6	$175.42	5.755%	$185.5154	$185.52	$185.50	$185.50
Purchase #7	$227.73	10.292%	$251.168	$251.17	$251.15	$251.20
7 purchase totals =	$800.89		$873.2709	$873.27	$873.15	$873.30