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	$24.97	13.827%	$28.4226	$28.42	$28.40	$28.40
Purchase #2	$227.52	7.599%	$244.8092	$244.81	$244.80	$244.80
Purchase #3	$42.77	13.600%	$48.5867	$48.59	$48.60	$48.60
Purchase #4	$163.71	10.835%	$181.448	$181.45	$181.45	$181.40
Purchase #5	$189.64	11.487%	$211.4239	$211.42	$211.40	$211.40
Purchase #6	$49.32	12.815%	$55.6404	$55.64	$55.65	$55.60
Purchase #7	$56.69	4.178%	$59.0585	$59.06	$59.05	$59.10
7 purchase totals =	$754.62		$829.3893	$829.39	$829.35	$829.30