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	$135.76	6.177%	$144.1459	$144.15	$144.15	$144.10
Purchase #2	$113.45	12.372%	$127.486	$127.49	$127.50	$127.50
Purchase #3	$8.86	5.762%	$9.3705	$9.37	$9.35	$9.40
Purchase #4	$12.43	4.376%	$12.9739	$12.97	$12.95	$13.00
Purchase #5	$102.48	10.408%	$113.1461	$113.15	$113.15	$113.10
Purchase #6	$220.72	9.745%	$242.2292	$242.23	$242.25	$242.20
Purchase #7	$105.29	5.586%	$111.1715	$111.17	$111.15	$111.20
7 purchase totals =	$698.99		$760.5231	$760.53	$760.50	$760.50