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	$205.86	3.359%	$212.7748	$212.77	$212.75	$212.80
Purchase #2	$240.30	13.762%	$273.3701	$273.37	$273.35	$273.40
Purchase #3	$142.84	12.718%	$161.0064	$161.01	$161.00	$161.00
Purchase #4	$190.61	3.136%	$196.5875	$196.59	$196.60	$196.60
Purchase #5	$38.43	10.475%	$42.4555	$42.46	$42.45	$42.50
Purchase #6	$111.54	7.204%	$119.5753	$119.58	$119.60	$119.60
Purchase #7	$58.73	11.387%	$65.4176	$65.42	$65.40	$65.40
7 purchase totals =	$988.31		$1,071.1872	$1,071.20	$1,071.15	$1,071.30