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	$74.61	13.445%	$84.6413	$84.64	$84.65	$84.60
Purchase #2	$139.25	6.661%	$148.5254	$148.53	$148.55	$148.50
Purchase #3	$104.77	11.544%	$116.8646	$116.86	$116.85	$116.90
Purchase #4	$218.47	11.143%	$242.8141	$242.81	$242.80	$242.80
Purchase #5	$137.70	3.286%	$142.2248	$142.22	$142.20	$142.20
Purchase #6	$139.70	10.662%	$154.5948	$154.59	$154.60	$154.60
Purchase #7	$75.69	3.228%	$78.1333	$78.13	$78.15	$78.10
7 purchase totals =	$890.19		$967.7983	$967.78	$967.80	$967.70