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	$123.29	13.666%	$140.1388	$140.14	$140.15	$140.10
Purchase #2	$227.39	11.517%	$253.5785	$253.58	$253.60	$253.60
Purchase #3	$148.31	5.137%	$155.9287	$155.93	$155.95	$155.90
Purchase #4	$54.49	11.775%	$60.9062	$60.91	$60.90	$60.90
Purchase #5	$100.94	3.383%	$104.3548	$104.35	$104.35	$104.40
Purchase #6	$19.81	3.240%	$20.4518	$20.45	$20.45	$20.50
Purchase #7	$115.54	11.151%	$128.4239	$128.42	$128.40	$128.40
7 purchase totals =	$789.77		$863.7827	$863.78	$863.80	$863.80