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	$231.36	10.439%	$255.5117	$255.51	$255.50	$255.50
Purchase #2	$221.54	8.704%	$240.8228	$240.82	$240.80	$240.80
Purchase #3	$125.51	4.835%	$131.5784	$131.58	$131.60	$131.60
Purchase #4	$24.25	9.699%	$26.602	$26.60	$26.60	$26.60
Purchase #5	$19.66	11.487%	$21.9183	$21.92	$21.90	$21.90
Purchase #6	$47.99	6.729%	$51.2192	$51.22	$51.20	$51.20
Purchase #7	$29.45	10.579%	$32.5655	$32.57	$32.55	$32.60
7 purchase totals =	$699.76		$760.2179	$760.22	$760.15	$760.20