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	$52.44	6.152%	$55.6661	$55.67	$55.65	$55.70
Purchase #2	$43.54	4.558%	$45.5246	$45.52	$45.50	$45.50
Purchase #3	$207.46	5.288%	$218.4305	$218.43	$218.45	$218.40
Purchase #4	$28.85	7.548%	$31.0276	$31.03	$31.05	$31.00
Purchase #5	$179.58	11.588%	$200.3897	$200.39	$200.40	$200.40
Purchase #6	$132.40	8.675%	$143.8857	$143.89	$143.90	$143.90
Purchase #7	$62.78	10.531%	$69.3914	$69.39	$69.40	$69.40
7 purchase totals =	$707.05		$764.3156	$764.32	$764.35	$764.30