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	$50.80	13.353%	$57.5833	$57.58	$57.60	$57.60
Purchase #2	$167.32	12.396%	$188.061	$188.06	$188.05	$188.10
Purchase #3	$42.72	13.130%	$48.3291	$48.33	$48.35	$48.30
Purchase #4	$31.62	3.168%	$32.6217	$32.62	$32.60	$32.60
Purchase #5	$34.59	12.231%	$38.8207	$38.82	$38.80	$38.80
Purchase #6	$164.57	5.406%	$173.4667	$173.47	$173.45	$173.50
Purchase #7	$44.96	12.372%	$50.5225	$50.52	$50.50	$50.50
7 purchase totals =	$536.58		$589.4050	$589.40	$589.35	$589.40