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	$235.54	8.624%	$255.853	$255.85	$255.85	$255.90
Purchase #2	$121.62	10.143%	$133.9559	$133.96	$133.95	$134.00
Purchase #3	$47.68	11.174%	$53.0078	$53.01	$53.00	$53.00
Purchase #4	$84.67	12.776%	$95.4874	$95.49	$95.50	$95.50
Purchase #5	$47.51	10.514%	$52.5052	$52.51	$52.50	$52.50
Purchase #6	$66.38	11.837%	$74.2374	$74.24	$74.25	$74.20
Purchase #7	$57.48	3.370%	$59.4171	$59.42	$59.40	$59.40
7 purchase totals =	$660.88		$724.4638	$724.48	$724.45	$724.50