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	$82.42	9.741%	$90.4485	$90.45	$90.45	$90.40
Purchase #2	$190.93	3.105%	$196.8584	$196.86	$196.85	$196.90
Purchase #3	$226.98	9.596%	$248.761	$248.76	$248.75	$248.80
Purchase #4	$46.54	12.830%	$52.5111	$52.51	$52.50	$52.50
Purchase #5	$17.35	5.296%	$18.2689	$18.27	$18.25	$18.30
Purchase #6	$128.35	12.129%	$143.9176	$143.92	$143.90	$143.90
Purchase #7	$171.25	9.211%	$187.0238	$187.02	$187.00	$187.00
7 purchase totals =	$863.82		$937.7893	$937.79	$937.70	$937.80