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	$230.67	7.721%	$248.48	$248.48	$248.50	$248.50
Purchase #2	$27.83	12.285%	$31.2489	$31.25	$31.25	$31.20
Purchase #3	$15.96	9.766%	$17.5187	$17.52	$17.50	$17.50
Purchase #4	$49.91	11.345%	$55.5723	$55.57	$55.55	$55.60
Purchase #5	$103.88	10.472%	$114.7583	$114.76	$114.75	$114.80
Purchase #6	$74.28	5.795%	$78.5845	$78.58	$78.60	$78.60
Purchase #7	$80.38	13.817%	$91.4861	$91.49	$91.50	$91.50
7 purchase totals =	$582.91		$637.6488	$637.65	$637.65	$637.70