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	$43.47	4.381%	$45.3744	$45.37	$45.35	$45.40
Purchase #2	$86.94	4.302%	$90.6802	$90.68	$90.70	$90.70
Purchase #3	$230.89	10.477%	$255.0803	$255.08	$255.10	$255.10
Purchase #4	$88.35	11.319%	$98.3503	$98.35	$98.35	$98.40
Purchase #5	$166.35	10.460%	$183.7502	$183.75	$183.75	$183.80
Purchase #6	$20.35	3.253%	$21.012	$21.01	$21.00	$21.00
Purchase #7	$136.86	6.619%	$145.9188	$145.92	$145.90	$145.90
7 purchase totals =	$773.21		$840.1662	$840.16	$840.15	$840.30