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	$49.57	13.631%	$56.3269	$56.33	$56.35	$56.30
Purchase #2	$97.49	11.848%	$109.0406	$109.04	$109.05	$109.00
Purchase #3	$75.43	10.545%	$83.3841	$83.38	$83.40	$83.40
Purchase #4	$95.51	4.583%	$99.8872	$99.89	$99.90	$99.90
Purchase #5	$81.58	10.602%	$90.2291	$90.23	$90.25	$90.20
Purchase #6	$201.85	6.836%	$215.6485	$215.65	$215.65	$215.60
Purchase #7	$156.89	5.102%	$164.8945	$164.89	$164.90	$164.90
7 purchase totals =	$758.32		$819.4109	$819.41	$819.50	$819.30