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	$19.62	10.588%	$21.6974	$21.70	$21.70	$21.70
Purchase #2	$48.43	3.638%	$50.1919	$50.19	$50.20	$50.20
Purchase #3	$20.27	5.309%	$21.3461	$21.35	$21.35	$21.30
Purchase #4	$240.43	12.642%	$270.8252	$270.83	$270.85	$270.80
Purchase #5	$109.39	6.852%	$116.8854	$116.89	$116.90	$116.90
Purchase #6	$36.59	6.635%	$39.0177	$39.02	$39.00	$39.00
Purchase #7	$126.34	12.466%	$142.0895	$142.09	$142.10	$142.10
7 purchase totals =	$601.07		$662.0532	$662.07	$662.10	$662.00