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	$24.50	10.536%	$27.0813	$27.08	$27.10	$27.10
Purchase #2	$38.40	11.602%	$42.8552	$42.86	$42.85	$42.90
Purchase #3	$37.75	13.702%	$42.9225	$42.92	$42.90	$42.90
Purchase #4	$244.75	11.143%	$272.0225	$272.02	$272.00	$272.00
Purchase #5	$148.39	11.447%	$165.3762	$165.38	$165.40	$165.40
Purchase #6	$19.49	11.143%	$21.6618	$21.66	$21.65	$21.70
Purchase #7	$142.43	9.502%	$155.9637	$155.96	$155.95	$156.00
7 purchase totals =	$655.71		$727.8832	$727.88	$727.85	$728.00