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	$230.74	11.688%	$257.7089	$257.71	$257.70	$257.70
Purchase #2	$12.85	3.223%	$13.2642	$13.26	$13.25	$13.30
Purchase #3	$27.30	6.160%	$28.9817	$28.98	$29.00	$29.00
Purchase #4	$72.33	12.359%	$81.2693	$81.27	$81.25	$81.30
Purchase #5	$87.82	3.231%	$90.6575	$90.66	$90.65	$90.70
Purchase #6	$12.98	7.335%	$13.9321	$13.93	$13.95	$13.90
Purchase #7	$66.51	10.419%	$73.4397	$73.44	$73.45	$73.40
7 purchase totals =	$510.53		$559.2534	$559.25	$559.25	$559.30