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	$38.50	12.110%	$43.1624	$43.16	$43.15	$43.20
Purchase #2	$12.37	9.667%	$13.5658	$13.57	$13.55	$13.60
Purchase #3	$218.34	10.599%	$241.4819	$241.48	$241.50	$241.50
Purchase #4	$69.68	12.592%	$78.4541	$78.45	$78.45	$78.50
Purchase #5	$244.43	6.254%	$259.7167	$259.72	$259.70	$259.70
Purchase #6	$120.63	8.685%	$131.1067	$131.11	$131.10	$131.10
Purchase #7	$73.90	10.348%	$81.5472	$81.55	$81.55	$81.50
7 purchase totals =	$777.85		$849.0348	$849.04	$849.00	$849.10