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	$157.86	13.134%	$178.5933	$178.59	$178.60	$178.60
Purchase #2	$202.61	12.843%	$228.6312	$228.63	$228.65	$228.60
Purchase #3	$234.29	9.479%	$256.4983	$256.50	$256.50	$256.50
Purchase #4	$14.35	4.683%	$15.022	$15.02	$15.00	$15.00
Purchase #5	$80.65	12.757%	$90.9385	$90.94	$90.95	$90.90
Purchase #6	$52.71	6.140%	$55.9464	$55.95	$55.95	$55.90
Purchase #7	$137.44	4.621%	$143.7911	$143.79	$143.80	$143.80
7 purchase totals =	$879.91		$969.4208	$969.42	$969.45	$969.30