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	$56.94	4.283%	$59.3787	$59.38	$59.40	$59.40
Purchase #2	$8.65	3.113%	$8.9193	$8.92	$8.90	$8.90
Purchase #3	$109.70	8.383%	$118.8962	$118.90	$118.90	$118.90
Purchase #4	$76.36	12.681%	$86.0432	$86.04	$86.05	$86.00
Purchase #5	$183.25	13.558%	$208.095	$208.10	$208.10	$208.10
Purchase #6	$50.91	3.820%	$52.8548	$52.85	$52.85	$52.90
Purchase #7	$103.31	9.611%	$113.2391	$113.24	$113.25	$113.20
7 purchase totals =	$589.12		$647.4263	$647.43	$647.45	$647.40