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	$66.40	5.825%	$70.2678	$70.27	$70.25	$70.30
Purchase #2	$166.54	13.156%	$188.45	$188.45	$188.45	$188.50
Purchase #3	$146.33	10.728%	$162.0283	$162.03	$162.05	$162.00
Purchase #4	$155.68	4.399%	$162.5284	$162.53	$162.55	$162.50
Purchase #5	$72.80	10.683%	$80.5772	$80.58	$80.60	$80.60
Purchase #6	$96.25	3.721%	$99.8315	$99.83	$99.85	$99.80
Purchase #7	$12.92	3.235%	$13.338	$13.34	$13.35	$13.30
7 purchase totals =	$716.92		$777.0212	$777.03	$777.10	$777.00