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	$35.48	12.384%	$39.8738	$39.87	$39.85	$39.90
Purchase #2	$22.82	10.171%	$25.141	$25.14	$25.15	$25.10
Purchase #3	$113.51	7.422%	$121.9347	$121.93	$121.95	$121.90
Purchase #4	$36.66	11.307%	$40.8051	$40.81	$40.80	$40.80
Purchase #5	$142.64	8.833%	$155.2394	$155.24	$155.25	$155.20
Purchase #6	$98.98	12.623%	$111.4742	$111.47	$111.45	$111.50
Purchase #7	$95.88	4.755%	$100.4391	$100.44	$100.45	$100.40
7 purchase totals =	$545.97		$594.9073	$594.90	$594.90	$594.80