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	$37.90	12.141%	$42.5014	$42.50	$42.50	$42.50
Purchase #2	$155.86	13.255%	$176.5192	$176.52	$176.50	$176.50
Purchase #3	$100.32	9.497%	$109.8474	$109.85	$109.85	$109.80
Purchase #4	$108.72	3.777%	$112.8264	$112.83	$112.85	$112.80
Purchase #5	$13.40	7.676%	$14.4286	$14.43	$14.45	$14.40
Purchase #6	$224.94	9.249%	$245.7447	$245.74	$245.75	$245.70
Purchase #7	$190.34	4.745%	$199.3716	$199.37	$199.35	$199.40
7 purchase totals =	$831.48		$901.2393	$901.24	$901.25	$901.10