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	$35.95	8.487%	$39.0011	$39.00	$39.00	$39.00
Purchase #2	$37.98	8.765%	$41.3089	$41.31	$41.30	$41.30
Purchase #3	$178.29	8.242%	$192.9847	$192.98	$193.00	$193.00
Purchase #4	$100.89	13.868%	$114.8814	$114.88	$114.90	$114.90
Purchase #5	$81.38	11.693%	$90.8958	$90.90	$90.90	$90.90
Purchase #6	$98.38	7.533%	$105.791	$105.79	$105.80	$105.80
Purchase #7	$162.42	8.858%	$176.8072	$176.81	$176.80	$176.80
7 purchase totals =	$695.29		$761.6701	$761.67	$761.70	$761.70