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	$36.41	10.771%	$40.3317	$40.33	$40.35	$40.30
Purchase #2	$57.86	8.269%	$62.6444	$62.64	$62.65	$62.60
Purchase #3	$176.80	13.343%	$200.3904	$200.39	$200.40	$200.40
Purchase #4	$153.48	10.696%	$169.8962	$169.90	$169.90	$169.90
Purchase #5	$109.82	6.250%	$116.6838	$116.68	$116.70	$116.70
Purchase #6	$103.30	13.416%	$117.1587	$117.16	$117.15	$117.20
Purchase #7	$95.86	4.633%	$100.3012	$100.30	$100.30	$100.30
7 purchase totals =	$733.53		$807.4064	$807.40	$807.45	$807.40