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	$25.27	10.365%	$27.8892	$27.89	$27.90	$27.90
Purchase #2	$27.38	11.103%	$30.42	$30.42	$30.40	$30.40
Purchase #3	$57.97	13.180%	$65.6104	$65.61	$65.60	$65.60
Purchase #4	$65.25	11.694%	$72.8803	$72.88	$72.90	$72.90
Purchase #5	$132.94	8.814%	$144.6573	$144.66	$144.65	$144.70
Purchase #6	$127.77	3.411%	$132.1282	$132.13	$132.15	$132.10
Purchase #7	$74.52	3.353%	$77.0187	$77.02	$77.00	$77.00
7 purchase totals =	$511.10		$550.6041	$550.61	$550.60	$550.60