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	$13.38	3.287%	$13.8198	$13.82	$13.80	$13.80
Purchase #2	$120.65	9.602%	$132.2348	$132.23	$132.25	$132.20
Purchase #3	$175.71	4.860%	$184.2495	$184.25	$184.25	$184.20
Purchase #4	$237.56	11.469%	$264.8058	$264.81	$264.80	$264.80
Purchase #5	$62.45	13.486%	$70.872	$70.87	$70.85	$70.90
Purchase #6	$132.82	6.739%	$141.7707	$141.77	$141.75	$141.80
Purchase #7	$39.75	7.784%	$42.8441	$42.84	$42.85	$42.80
7 purchase totals =	$782.32		$850.5967	$850.59	$850.55	$850.50