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	$157.80	10.575%	$174.4874	$174.49	$174.50	$174.50
Purchase #2	$199.59	3.333%	$206.2423	$206.24	$206.25	$206.20
Purchase #3	$50.98	13.102%	$57.6594	$57.66	$57.65	$57.70
Purchase #4	$143.93	9.804%	$158.0409	$158.04	$158.05	$158.00
Purchase #5	$40.62	11.408%	$45.2539	$45.25	$45.25	$45.30
Purchase #6	$92.32	9.212%	$100.8245	$100.82	$100.80	$100.80
Purchase #7	$111.95	13.337%	$126.8808	$126.88	$126.90	$126.90
7 purchase totals =	$797.19		$869.3892	$869.38	$869.40	$869.40