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	$8.39	3.489%	$8.6827	$8.68	$8.70	$8.70
Purchase #2	$99.29	10.734%	$109.9478	$109.95	$109.95	$109.90
Purchase #3	$18.46	9.105%	$20.1408	$20.14	$20.15	$20.10
Purchase #4	$153.31	8.166%	$165.8293	$165.83	$165.85	$165.80
Purchase #5	$190.54	4.723%	$199.5392	$199.54	$199.55	$199.50
Purchase #6	$124.71	9.683%	$136.7857	$136.79	$136.80	$136.80
Purchase #7	$222.59	12.127%	$249.5835	$249.58	$249.60	$249.60
7 purchase totals =	$817.29		$890.5090	$890.51	$890.60	$890.40