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	$227.30	13.836%	$258.7492	$258.75	$258.75	$258.70
Purchase #2	$47.26	11.685%	$52.7823	$52.78	$52.80	$52.80
Purchase #3	$105.28	6.256%	$111.8663	$111.87	$111.85	$111.90
Purchase #4	$111.26	11.486%	$124.0393	$124.04	$124.05	$124.00
Purchase #5	$19.61	9.228%	$21.4196	$21.42	$21.40	$21.40
Purchase #6	$13.64	9.533%	$14.9403	$14.94	$14.95	$14.90
Purchase #7	$13.39	7.751%	$14.4279	$14.43	$14.45	$14.40
7 purchase totals =	$537.74		$598.2249	$598.23	$598.25	$598.10