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	$171.59	3.667%	$177.8822	$177.88	$177.90	$177.90
Purchase #2	$97.92	11.572%	$109.2513	$109.25	$109.25	$109.30
Purchase #3	$125.93	5.814%	$133.2516	$133.25	$133.25	$133.30
Purchase #4	$100.38	4.383%	$104.7797	$104.78	$104.80	$104.80
Purchase #5	$88.96	13.451%	$100.926	$100.93	$100.95	$100.90
Purchase #6	$59.70	7.783%	$64.3465	$64.35	$64.35	$64.30
Purchase #7	$118.96	10.133%	$131.0142	$131.01	$131.00	$131.00
7 purchase totals =	$763.44		$821.4515	$821.45	$821.50	$821.50