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	$6.34	7.102%	$6.7903	$6.79	$6.80	$6.80
Purchase #2	$159.93	3.329%	$165.2541	$165.25	$165.25	$165.30
Purchase #3	$111.93	10.409%	$123.5808	$123.58	$123.60	$123.60
Purchase #4	$38.62	3.400%	$39.9331	$39.93	$39.95	$39.90
Purchase #5	$15.39	13.859%	$17.5229	$17.52	$17.50	$17.50
Purchase #6	$192.90	10.461%	$213.0793	$213.08	$213.10	$213.10
Purchase #7	$85.72	4.443%	$89.5285	$89.53	$89.55	$89.50
7 purchase totals =	$610.83		$655.6890	$655.68	$655.75	$655.70