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	$95.96	5.131%	$100.8837	$100.88	$100.90	$100.90
Purchase #2	$50.36	4.252%	$52.5013	$52.50	$52.50	$52.50
Purchase #3	$136.55	6.456%	$145.3657	$145.37	$145.35	$145.40
Purchase #4	$106.31	9.821%	$116.7507	$116.75	$116.75	$116.80
Purchase #5	$35.48	9.519%	$38.8573	$38.86	$38.85	$38.90
Purchase #6	$202.39	3.208%	$208.8827	$208.88	$208.90	$208.90
Purchase #7	$24.44	5.189%	$25.7082	$25.71	$25.70	$25.70
7 purchase totals =	$651.49		$688.9496	$688.95	$688.95	$689.10