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	$52.35	8.333%	$56.7123	$56.71	$56.70	$56.70
Purchase #2	$132.26	9.277%	$144.5298	$144.53	$144.55	$144.50
Purchase #3	$231.84	10.546%	$256.2898	$256.29	$256.30	$256.30
Purchase #4	$120.36	11.842%	$134.613	$134.61	$134.60	$134.60
Purchase #5	$144.70	5.357%	$152.4516	$152.45	$152.45	$152.50
Purchase #6	$81.94	5.622%	$86.5467	$86.55	$86.55	$86.50
Purchase #7	$247.46	8.857%	$269.3775	$269.38	$269.40	$269.40
7 purchase totals =	$1,010.91		$1,100.5207	$1,100.52	$1,100.55	$1,100.50