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	$36.86	6.801%	$39.3668	$39.37	$39.35	$39.40
Purchase #2	$146.51	13.333%	$166.0442	$166.04	$166.05	$166.00
Purchase #3	$227.47	13.104%	$257.2777	$257.28	$257.30	$257.30
Purchase #4	$195.39	7.652%	$210.3412	$210.34	$210.35	$210.30
Purchase #5	$244.52	4.859%	$256.4012	$256.40	$256.40	$256.40
Purchase #6	$131.33	13.130%	$148.5736	$148.57	$148.55	$148.60
Purchase #7	$57.75	8.289%	$62.5369	$62.54	$62.55	$62.50
7 purchase totals =	$1,039.83		$1,140.5416	$1,140.54	$1,140.55	$1,140.50