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	$15.46	9.605%	$16.9449	$16.94	$16.95	$16.90
Purchase #2	$117.28	10.264%	$129.3176	$129.32	$129.30	$129.30
Purchase #3	$23.49	5.832%	$24.8599	$24.86	$24.85	$24.90
Purchase #4	$160.37	9.511%	$175.6228	$175.62	$175.60	$175.60
Purchase #5	$86.66	3.208%	$89.4401	$89.44	$89.45	$89.40
Purchase #6	$81.87	9.125%	$89.3406	$89.34	$89.35	$89.30
Purchase #7	$132.72	8.444%	$143.9269	$143.93	$143.95	$143.90
7 purchase totals =	$617.85		$669.4528	$669.45	$669.45	$669.30