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	$39.37	13.335%	$44.62	$44.62	$44.60	$44.60
Purchase #2	$187.71	4.848%	$196.8102	$196.81	$196.80	$196.80
Purchase #3	$36.86	7.221%	$39.5217	$39.52	$39.50	$39.50
Purchase #4	$18.64	12.308%	$20.9342	$20.93	$20.95	$20.90
Purchase #5	$232.52	12.387%	$261.3223	$261.32	$261.30	$261.30
Purchase #6	$52.38	9.679%	$57.4499	$57.45	$57.45	$57.40
Purchase #7	$242.52	9.375%	$265.2563	$265.26	$265.25	$265.30
7 purchase totals =	$810.00		$885.9146	$885.91	$885.85	$885.80