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	$135.77	10.536%	$150.0747	$150.07	$150.05	$150.10
Purchase #2	$67.50	8.788%	$73.4319	$73.43	$73.45	$73.40
Purchase #3	$125.86	12.390%	$141.4541	$141.45	$141.45	$141.50
Purchase #4	$249.71	5.420%	$263.2443	$263.24	$263.25	$263.20
Purchase #5	$67.59	8.373%	$73.2493	$73.25	$73.25	$73.20
Purchase #6	$118.34	4.291%	$123.418	$123.42	$123.40	$123.40
Purchase #7	$20.84	3.315%	$21.5308	$21.53	$21.55	$21.50
7 purchase totals =	$785.61		$846.4031	$846.39	$846.40	$846.30