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	$243.70	10.579%	$269.481	$269.48	$269.50	$269.50
Purchase #2	$176.85	3.612%	$183.2378	$183.24	$183.25	$183.20
Purchase #3	$10.27	9.655%	$11.2616	$11.26	$11.25	$11.30
Purchase #4	$34.39	11.673%	$38.4043	$38.40	$38.40	$38.40
Purchase #5	$198.49	13.287%	$224.8634	$224.86	$224.85	$224.90
Purchase #6	$6.81	11.558%	$7.5971	$7.60	$7.60	$7.60
Purchase #7	$235.76	3.335%	$243.6226	$243.62	$243.60	$243.60
7 purchase totals =	$906.27		$978.4678	$978.46	$978.45	$978.50