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	$96.82	7.855%	$104.4252	$104.43	$104.45	$104.40
Purchase #2	$52.81	12.847%	$59.5945	$59.59	$59.60	$59.60
Purchase #3	$8.59	7.669%	$9.2488	$9.25	$9.25	$9.20
Purchase #4	$162.75	12.342%	$182.8366	$182.84	$182.85	$182.80
Purchase #5	$54.61	12.647%	$61.5165	$61.52	$61.50	$61.50
Purchase #6	$150.76	11.172%	$167.6029	$167.60	$167.60	$167.60
Purchase #7	$227.42	13.385%	$257.8602	$257.86	$257.85	$257.90
7 purchase totals =	$753.76		$843.0847	$843.09	$843.10	$843.00