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	$250.99	9.785%	$275.5494	$275.55	$275.55	$275.50
Purchase #2	$179.93	9.445%	$196.9244	$196.92	$196.90	$196.90
Purchase #3	$15.46	5.194%	$16.263	$16.26	$16.25	$16.30
Purchase #4	$48.61	8.864%	$52.9188	$52.92	$52.90	$52.90
Purchase #5	$50.43	7.161%	$54.0413	$54.04	$54.05	$54.00
Purchase #6	$113.90	5.123%	$119.7351	$119.74	$119.75	$119.70
Purchase #7	$100.59	12.717%	$113.382	$113.38	$113.40	$113.40
7 purchase totals =	$759.91		$828.8140	$828.81	$828.80	$828.70