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	$180.82	4.566%	$189.0762	$189.08	$189.10	$189.10
Purchase #2	$108.65	13.561%	$123.384	$123.38	$123.40	$123.40
Purchase #3	$82.89	9.212%	$90.5258	$90.53	$90.55	$90.50
Purchase #4	$36.98	9.330%	$40.4302	$40.43	$40.45	$40.40
Purchase #5	$101.67	5.228%	$106.9853	$106.99	$107.00	$107.00
Purchase #6	$61.42	12.134%	$68.8727	$68.87	$68.85	$68.90
Purchase #7	$175.66	5.189%	$184.775	$184.78	$184.80	$184.80
7 purchase totals =	$748.09		$804.0492	$804.06	$804.15	$804.10