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	$130.25	6.716%	$138.9976	$139.00	$139.00	$139.00
Purchase #2	$164.46	12.600%	$185.182	$185.18	$185.20	$185.20
Purchase #3	$127.31	10.675%	$140.9003	$140.90	$140.90	$140.90
Purchase #4	$128.62	10.508%	$142.1354	$142.14	$142.15	$142.10
Purchase #5	$87.34	10.843%	$96.8103	$96.81	$96.80	$96.80
Purchase #6	$137.64	4.478%	$143.8035	$143.80	$143.80	$143.80
Purchase #7	$232.35	10.577%	$256.9257	$256.93	$256.95	$256.90
7 purchase totals =	$1,007.97		$1,104.7548	$1,104.76	$1,104.80	$1,104.70