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	$125.27	9.723%	$137.45	$137.45	$137.45	$137.50
Purchase #2	$240.27	8.662%	$261.0822	$261.08	$261.10	$261.10
Purchase #3	$142.50	5.589%	$150.4643	$150.46	$150.45	$150.50
Purchase #4	$124.95	10.330%	$137.8573	$137.86	$137.85	$137.90
Purchase #5	$31.49	7.481%	$33.8458	$33.85	$33.85	$33.80
Purchase #6	$51.78	9.400%	$56.6473	$56.65	$56.65	$56.60
Purchase #7	$127.35	5.411%	$134.2409	$134.24	$134.25	$134.20
7 purchase totals =	$843.61		$911.5878	$911.59	$911.60	$911.60