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	$50.79	11.549%	$56.6557	$56.66	$56.65	$56.70
Purchase #2	$210.92	10.159%	$232.3474	$232.35	$232.35	$232.30
Purchase #3	$131.71	4.632%	$137.8108	$137.81	$137.80	$137.80
Purchase #4	$147.59	7.323%	$158.398	$158.40	$158.40	$158.40
Purchase #5	$193.75	3.641%	$200.8044	$200.80	$200.80	$200.80
Purchase #6	$169.81	12.183%	$190.498	$190.50	$190.50	$190.50
Purchase #7	$28.80	10.270%	$31.7578	$31.76	$31.75	$31.80
7 purchase totals =	$933.37		$1,008.2721	$1,008.28	$1,008.25	$1,008.30