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	$162.92	12.617%	$183.4756	$183.48	$183.50	$183.50
Purchase #2	$45.74	5.473%	$48.2434	$48.24	$48.25	$48.20
Purchase #3	$100.65	3.215%	$103.8859	$103.89	$103.90	$103.90
Purchase #4	$217.70	8.624%	$236.4744	$236.47	$236.45	$236.50
Purchase #5	$34.57	12.365%	$38.8446	$38.84	$38.85	$38.80
Purchase #6	$173.77	10.217%	$191.5241	$191.52	$191.50	$191.50
Purchase #7	$165.76	7.575%	$178.3163	$178.32	$178.30	$178.30
7 purchase totals =	$901.11		$980.7643	$980.76	$980.75	$980.70