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	$140.44	12.870%	$158.5146	$158.51	$158.50	$158.50
Purchase #2	$44.78	8.530%	$48.5997	$48.60	$48.60	$48.60
Purchase #3	$157.76	9.372%	$172.5453	$172.55	$172.55	$172.50
Purchase #4	$108.96	6.772%	$116.3388	$116.34	$116.35	$116.30
Purchase #5	$111.94	11.225%	$124.5053	$124.51	$124.50	$124.50
Purchase #6	$186.34	9.210%	$203.5019	$203.50	$203.50	$203.50
Purchase #7	$72.71	7.663%	$78.2818	$78.28	$78.30	$78.30
7 purchase totals =	$822.93		$902.2874	$902.29	$902.30	$902.20