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	$13.57	13.364%	$15.3835	$15.38	$15.40	$15.40
Purchase #2	$158.59	5.193%	$166.8256	$166.83	$166.85	$166.80
Purchase #3	$183.46	3.369%	$189.6408	$189.64	$189.65	$189.60
Purchase #4	$6.80	11.644%	$7.5918	$7.59	$7.60	$7.60
Purchase #5	$165.84	10.317%	$182.9497	$182.95	$182.95	$182.90
Purchase #6	$40.92	4.758%	$42.867	$42.87	$42.85	$42.90
Purchase #7	$13.82	6.269%	$14.6864	$14.69	$14.70	$14.70
7 purchase totals =	$583.00		$619.9448	$619.95	$620.00	$619.90