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	$20.88	9.800%	$22.9262	$22.93	$22.95	$22.90
Purchase #2	$114.61	4.308%	$119.5474	$119.55	$119.55	$119.50
Purchase #3	$43.64	4.152%	$45.4519	$45.45	$45.45	$45.50
Purchase #4	$160.58	9.846%	$176.3907	$176.39	$176.40	$176.40
Purchase #5	$110.46	10.184%	$121.7092	$121.71	$121.70	$121.70
Purchase #6	$18.33	11.604%	$20.457	$20.46	$20.45	$20.50
Purchase #7	$126.63	13.308%	$143.4819	$143.48	$143.50	$143.50
7 purchase totals =	$595.13		$649.9643	$649.97	$650.00	$650.00