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	$50.98	9.144%	$55.6416	$55.64	$55.65	$55.60
Purchase #2	$139.96	13.469%	$158.8112	$158.81	$158.80	$158.80
Purchase #3	$73.29	7.539%	$78.8153	$78.82	$78.80	$78.80
Purchase #4	$132.34	10.772%	$146.5957	$146.60	$146.60	$146.60
Purchase #5	$214.86	12.217%	$241.1094	$241.11	$241.10	$241.10
Purchase #6	$90.40	4.571%	$94.5322	$94.53	$94.55	$94.50
Purchase #7	$121.81	12.814%	$137.4187	$137.42	$137.40	$137.40
7 purchase totals =	$823.64		$912.9241	$912.93	$912.90	$912.80