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	$245.77	5.288%	$258.7663	$258.77	$258.75	$258.80
Purchase #2	$221.50	10.336%	$244.3942	$244.39	$244.40	$244.40
Purchase #3	$12.58	13.238%	$14.2453	$14.25	$14.25	$14.20
Purchase #4	$42.50	12.419%	$47.7781	$47.78	$47.80	$47.80
Purchase #5	$80.30	13.715%	$91.3131	$91.31	$91.30	$91.30
Purchase #6	$137.43	4.505%	$143.6212	$143.62	$143.60	$143.60
Purchase #7	$65.52	9.269%	$71.593	$71.59	$71.60	$71.60
7 purchase totals =	$805.60		$871.7112	$871.71	$871.70	$871.70