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	$54.71	3.463%	$56.6046	$56.60	$56.60	$56.60
Purchase #2	$96.75	9.116%	$105.5697	$105.57	$105.55	$105.60
Purchase #3	$148.96	7.264%	$159.7805	$159.78	$159.80	$159.80
Purchase #4	$221.37	9.585%	$242.5883	$242.59	$242.60	$242.60
Purchase #5	$23.42	4.608%	$24.4992	$24.50	$24.50	$24.50
Purchase #6	$52.58	13.569%	$59.7146	$59.71	$59.70	$59.70
Purchase #7	$39.43	10.337%	$43.5059	$43.51	$43.50	$43.50
7 purchase totals =	$637.22		$692.2628	$692.26	$692.25	$692.30