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	$38.44	12.671%	$43.3107	$43.31	$43.30	$43.30
Purchase #2	$116.38	6.496%	$123.94	$123.94	$123.95	$123.90
Purchase #3	$167.60	8.872%	$182.4695	$182.47	$182.45	$182.50
Purchase #4	$119.40	11.218%	$132.7943	$132.79	$132.80	$132.80
Purchase #5	$85.57	6.127%	$90.8129	$90.81	$90.80	$90.80
Purchase #6	$241.85	5.647%	$255.5073	$255.51	$255.50	$255.50
Purchase #7	$185.72	7.166%	$199.0287	$199.03	$199.05	$199.00
7 purchase totals =	$954.96		$1,027.8634	$1,027.86	$1,027.85	$1,027.80