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	$135.63	6.602%	$144.5843	$144.58	$144.60	$144.60
Purchase #2	$60.91	8.803%	$66.2719	$66.27	$66.25	$66.30
Purchase #3	$238.76	7.151%	$255.8337	$255.83	$255.85	$255.80
Purchase #4	$51.98	3.168%	$53.6267	$53.63	$53.65	$53.60
Purchase #5	$19.76	10.393%	$21.8137	$21.81	$21.80	$21.80
Purchase #6	$100.73	9.557%	$110.3568	$110.36	$110.35	$110.40
Purchase #7	$106.49	6.687%	$113.611	$113.61	$113.60	$113.60
7 purchase totals =	$714.26		$766.0981	$766.09	$766.10	$766.10