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	$79.49	13.435%	$90.1695	$90.17	$90.15	$90.20
Purchase #2	$101.59	6.290%	$107.98	$107.98	$108.00	$108.00
Purchase #3	$65.85	10.448%	$72.73	$72.73	$72.75	$72.70
Purchase #4	$39.60	7.192%	$42.448	$42.45	$42.45	$42.40
Purchase #5	$192.56	5.722%	$203.5783	$203.58	$203.60	$203.60
Purchase #6	$144.66	8.480%	$156.9272	$156.93	$156.95	$156.90
Purchase #7	$63.29	11.267%	$70.4209	$70.42	$70.40	$70.40
7 purchase totals =	$687.04		$744.2539	$744.26	$744.30	$744.20