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	$31.91	13.763%	$36.3018	$36.30	$36.30	$36.30
Purchase #2	$67.45	4.555%	$70.5223	$70.52	$70.50	$70.50
Purchase #3	$82.44	9.531%	$90.2974	$90.30	$90.30	$90.30
Purchase #4	$135.90	5.819%	$143.808	$143.81	$143.80	$143.80
Purchase #5	$70.81	4.635%	$74.092	$74.09	$74.10	$74.10
Purchase #6	$103.86	10.249%	$114.5046	$114.50	$114.50	$114.50
Purchase #7	$56.59	3.288%	$58.4507	$58.45	$58.45	$58.50
7 purchase totals =	$548.96		$587.9768	$587.97	$587.95	$588.00