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	$240.63	13.664%	$273.5097	$273.51	$273.50	$273.50
Purchase #2	$238.93	11.422%	$266.2206	$266.22	$266.20	$266.20
Purchase #3	$246.40	13.523%	$279.7207	$279.72	$279.70	$279.70
Purchase #4	$184.44	11.153%	$205.0106	$205.01	$205.00	$205.00
Purchase #5	$80.72	11.704%	$90.1675	$90.17	$90.15	$90.20
Purchase #6	$56.82	3.300%	$58.6951	$58.70	$58.70	$58.70
Purchase #7	$122.59	7.262%	$131.4925	$131.49	$131.50	$131.50
7 purchase totals =	$1,170.53		$1,304.8167	$1,304.82	$1,304.75	$1,304.80