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	$38.59	13.773%	$43.905	$43.91	$43.90	$43.90
Purchase #2	$37.89	4.366%	$39.5443	$39.54	$39.55	$39.50
Purchase #3	$70.40	13.121%	$79.6372	$79.64	$79.65	$79.60
Purchase #4	$64.66	3.534%	$66.9451	$66.95	$66.95	$66.90
Purchase #5	$44.28	10.463%	$48.913	$48.91	$48.90	$48.90
Purchase #6	$116.78	3.697%	$121.0974	$121.10	$121.10	$121.10
Purchase #7	$142.27	12.300%	$159.7692	$159.77	$159.75	$159.80
7 purchase totals =	$514.87		$559.8112	$559.82	$559.80	$559.70