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	$46.96	3.805%	$48.7468	$48.75	$48.75	$48.70
Purchase #2	$144.83	13.771%	$164.7745	$164.77	$164.75	$164.80
Purchase #3	$75.81	6.334%	$80.6118	$80.61	$80.60	$80.60
Purchase #4	$79.64	5.240%	$83.8131	$83.81	$83.80	$83.80
Purchase #5	$61.72	8.283%	$66.8323	$66.83	$66.85	$66.80
Purchase #6	$166.77	13.681%	$189.5858	$189.59	$189.60	$189.60
Purchase #7	$17.29	13.297%	$19.5891	$19.59	$19.60	$19.60
7 purchase totals =	$593.02		$653.9534	$653.95	$653.95	$653.90