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	$92.47	8.375%	$100.2144	$100.21	$100.20	$100.20
Purchase #2	$71.54	10.128%	$78.7856	$78.79	$78.80	$78.80
Purchase #3	$65.31	11.512%	$72.8285	$72.83	$72.85	$72.80
Purchase #4	$103.60	5.157%	$108.9427	$108.94	$108.95	$108.90
Purchase #5	$64.27	12.629%	$72.3867	$72.39	$72.40	$72.40
Purchase #6	$230.50	10.130%	$253.8497	$253.85	$253.85	$253.80
Purchase #7	$134.52	7.769%	$144.9709	$144.97	$144.95	$145.00
7 purchase totals =	$762.21		$831.9785	$831.98	$832.00	$831.90