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	$40.45	5.735%	$42.7698	$42.77	$42.75	$42.80
Purchase #2	$128.35	11.640%	$143.2899	$143.29	$143.30	$143.30
Purchase #3	$137.67	3.491%	$142.4761	$142.48	$142.50	$142.50
Purchase #4	$229.68	6.207%	$243.9362	$243.94	$243.95	$243.90
Purchase #5	$100.35	13.218%	$113.6143	$113.61	$113.60	$113.60
Purchase #6	$154.65	10.285%	$170.5558	$170.56	$170.55	$170.60
Purchase #7	$121.26	4.540%	$126.7652	$126.77	$126.75	$126.80
7 purchase totals =	$912.41		$983.4073	$983.42	$983.40	$983.50