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	$241.52	6.401%	$256.9797	$256.98	$257.00	$257.00
Purchase #2	$237.95	3.775%	$246.9326	$246.93	$246.95	$246.90
Purchase #3	$158.96	5.263%	$167.3261	$167.33	$167.35	$167.30
Purchase #4	$48.32	11.769%	$54.0068	$54.01	$54.00	$54.00
Purchase #5	$90.28	4.426%	$94.2758	$94.28	$94.30	$94.30
Purchase #6	$46.43	9.353%	$50.7726	$50.77	$50.75	$50.80
Purchase #7	$90.61	10.627%	$100.2391	$100.24	$100.25	$100.20
7 purchase totals =	$914.07		$970.5327	$970.54	$970.60	$970.50