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	$37.56	8.756%	$40.8488	$40.85	$40.85	$40.80
Purchase #2	$217.63	13.210%	$246.3789	$246.38	$246.40	$246.40
Purchase #3	$161.63	5.553%	$170.6053	$170.61	$170.60	$170.60
Purchase #4	$111.68	4.410%	$116.6051	$116.61	$116.60	$116.60
Purchase #5	$50.30	6.427%	$53.5328	$53.53	$53.55	$53.50
Purchase #6	$50.86	13.135%	$57.5405	$57.54	$57.55	$57.50
Purchase #7	$18.60	10.248%	$20.5061	$20.51	$20.50	$20.50
7 purchase totals =	$648.26		$706.0175	$706.03	$706.05	$705.90