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	$36.56	6.149%	$38.8081	$38.81	$38.80	$38.80
Purchase #2	$15.52	12.210%	$17.415	$17.42	$17.40	$17.40
Purchase #3	$244.80	4.695%	$256.2934	$256.29	$256.30	$256.30
Purchase #4	$247.64	13.167%	$280.2468	$280.25	$280.25	$280.20
Purchase #5	$100.70	3.221%	$103.9435	$103.94	$103.95	$103.90
Purchase #6	$50.29	7.770%	$54.1975	$54.20	$54.20	$54.20
Purchase #7	$119.27	4.144%	$124.2125	$124.21	$124.20	$124.20
7 purchase totals =	$814.78		$875.1168	$875.12	$875.10	$875.00