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	$22.38	9.467%	$24.4987	$24.50	$24.50	$24.50
Purchase #2	$154.40	4.629%	$161.5472	$161.55	$161.55	$161.50
Purchase #3	$43.28	5.706%	$45.7496	$45.75	$45.75	$45.70
Purchase #4	$48.67	6.612%	$51.8881	$51.89	$51.90	$51.90
Purchase #5	$182.40	9.354%	$199.4617	$199.46	$199.45	$199.50
Purchase #6	$113.65	11.217%	$126.3981	$126.40	$126.40	$126.40
Purchase #7	$85.50	5.533%	$90.2307	$90.23	$90.25	$90.20
7 purchase totals =	$650.28		$699.7741	$699.78	$699.80	$699.70