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	$227.26	5.826%	$240.5002	$240.50	$240.50	$240.50
Purchase #2	$115.29	5.452%	$121.5756	$121.58	$121.60	$121.60
Purchase #3	$96.44	3.494%	$99.8096	$99.81	$99.80	$99.80
Purchase #4	$142.33	9.559%	$155.9353	$155.94	$155.95	$155.90
Purchase #5	$97.47	6.200%	$103.5131	$103.51	$103.50	$103.50
Purchase #6	$73.72	12.469%	$82.9121	$82.91	$82.90	$82.90
Purchase #7	$103.99	10.265%	$114.6646	$114.66	$114.65	$114.70
7 purchase totals =	$856.50		$918.9105	$918.91	$918.90	$918.90