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	$82.67	9.728%	$90.7121	$90.71	$90.70	$90.70
Purchase #2	$136.39	7.398%	$146.4801	$146.48	$146.50	$146.50
Purchase #3	$180.67	10.342%	$199.3549	$199.35	$199.35	$199.40
Purchase #4	$49.85	4.198%	$51.9427	$51.94	$51.95	$51.90
Purchase #5	$29.46	6.491%	$31.3722	$31.37	$31.35	$31.40
Purchase #6	$68.73	13.357%	$77.9103	$77.91	$77.90	$77.90
Purchase #7	$82.30	5.367%	$86.717	$86.72	$86.70	$86.70
7 purchase totals =	$630.07		$684.4893	$684.48	$684.45	$684.50