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	$103.32	9.242%	$112.8688	$112.87	$112.85	$112.90
Purchase #2	$177.40	3.321%	$183.2915	$183.29	$183.30	$183.30
Purchase #3	$119.92	5.710%	$126.7674	$126.77	$126.75	$126.80
Purchase #4	$125.43	13.336%	$142.1573	$142.16	$142.15	$142.20
Purchase #5	$124.70	6.729%	$133.0911	$133.09	$133.10	$133.10
Purchase #6	$141.88	4.858%	$148.7725	$148.77	$148.75	$148.80
Purchase #7	$85.33	6.497%	$90.8739	$90.87	$90.85	$90.90
7 purchase totals =	$877.98		$937.8225	$937.82	$937.75	$938.00