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	$74.54	9.137%	$81.3507	$81.35	$81.35	$81.40
Purchase #2	$146.60	10.456%	$161.9285	$161.93	$161.95	$161.90
Purchase #3	$66.51	8.277%	$72.015	$72.02	$72.00	$72.00
Purchase #4	$187.25	3.795%	$194.3561	$194.36	$194.35	$194.40
Purchase #5	$65.53	10.859%	$72.6459	$72.65	$72.65	$72.60
Purchase #6	$30.45	4.776%	$31.9043	$31.90	$31.90	$31.90
Purchase #7	$66.80	5.359%	$70.3798	$70.38	$70.40	$70.40
7 purchase totals =	$637.68		$684.5803	$684.59	$684.60	$684.60