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	$85.63	5.458%	$90.3037	$90.30	$90.30	$90.30
Purchase #2	$175.65	4.570%	$183.6772	$183.68	$183.70	$183.70
Purchase #3	$132.74	7.333%	$142.4738	$142.47	$142.45	$142.50
Purchase #4	$38.88	10.409%	$42.927	$42.93	$42.95	$42.90
Purchase #5	$19.85	7.150%	$21.2693	$21.27	$21.25	$21.30
Purchase #6	$203.31	10.291%	$224.2326	$224.23	$224.25	$224.20
Purchase #7	$70.40	3.455%	$72.8323	$72.83	$72.85	$72.80
7 purchase totals =	$726.46		$777.7159	$777.71	$777.75	$777.70