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	$181.59	10.584%	$200.8095	$200.81	$200.80	$200.80
Purchase #2	$51.76	5.688%	$54.7041	$54.70	$54.70	$54.70
Purchase #3	$211.48	12.244%	$237.3736	$237.37	$237.35	$237.40
Purchase #4	$128.56	4.871%	$134.8222	$134.82	$134.80	$134.80
Purchase #5	$27.33	7.798%	$29.4612	$29.46	$29.45	$29.50
Purchase #6	$124.95	11.853%	$139.7603	$139.76	$139.75	$139.80
Purchase #7	$29.69	9.783%	$32.5946	$32.59	$32.60	$32.60
7 purchase totals =	$755.36		$829.5255	$829.51	$829.45	$829.60