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	$138.45	5.735%	$146.3901	$146.39	$146.40	$146.40
Purchase #2	$134.39	12.372%	$151.0167	$151.02	$151.00	$151.00
Purchase #3	$74.40	10.747%	$82.3958	$82.40	$82.40	$82.40
Purchase #4	$103.51	11.285%	$115.1911	$115.19	$115.20	$115.20
Purchase #5	$12.76	4.746%	$13.3656	$13.37	$13.35	$13.40
Purchase #6	$234.71	8.677%	$255.0758	$255.08	$255.10	$255.10
Purchase #7	$39.48	7.786%	$42.5539	$42.55	$42.55	$42.60
7 purchase totals =	$737.70		$805.9890	$806.00	$806.00	$806.10