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	$243.81	6.758%	$260.2867	$260.29	$260.30	$260.30
Purchase #2	$16.40	11.725%	$18.3229	$18.32	$18.30	$18.30
Purchase #3	$60.79	9.549%	$66.5948	$66.59	$66.60	$66.60
Purchase #4	$162.95	5.360%	$171.6841	$171.68	$171.70	$171.70
Purchase #5	$121.58	10.548%	$134.4043	$134.40	$134.40	$134.40
Purchase #6	$37.35	4.143%	$38.8974	$38.90	$38.90	$38.90
Purchase #7	$73.43	13.414%	$83.2799	$83.28	$83.30	$83.30
7 purchase totals =	$716.31		$773.4701	$773.46	$773.50	$773.50