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	$126.92	3.703%	$131.6198	$131.62	$131.60	$131.60
Purchase #2	$173.26	3.772%	$179.7954	$179.80	$179.80	$179.80
Purchase #3	$48.97	11.703%	$54.701	$54.70	$54.70	$54.70
Purchase #4	$29.36	7.773%	$31.6422	$31.64	$31.65	$31.60
Purchase #5	$238.46	7.382%	$256.0631	$256.06	$256.05	$256.10
Purchase #6	$95.60	8.600%	$103.8216	$103.82	$103.80	$103.80
Purchase #7	$53.72	4.588%	$56.1847	$56.18	$56.20	$56.20
7 purchase totals =	$766.29		$813.8278	$813.82	$813.80	$813.80