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	$166.99	9.669%	$183.1363	$183.14	$183.15	$183.10
Purchase #2	$153.58	6.757%	$163.9574	$163.96	$163.95	$164.00
Purchase #3	$39.96	6.703%	$42.6385	$42.64	$42.65	$42.60
Purchase #4	$80.83	13.605%	$91.8269	$91.83	$91.85	$91.80
Purchase #5	$196.27	11.559%	$218.9568	$218.96	$218.95	$219.00
Purchase #6	$128.56	13.145%	$145.4592	$145.46	$145.45	$145.50
Purchase #7	$112.26	13.837%	$127.7934	$127.79	$127.80	$127.80
7 purchase totals =	$878.45		$973.7685	$973.78	$973.80	$973.80