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	$146.86	8.617%	$159.5149	$159.51	$159.50	$159.50
Purchase #2	$30.54	4.317%	$31.8584	$31.86	$31.85	$31.90
Purchase #3	$116.33	9.671%	$127.5803	$127.58	$127.60	$127.60
Purchase #4	$21.58	5.666%	$22.8027	$22.80	$22.80	$22.80
Purchase #5	$114.92	11.554%	$128.1979	$128.20	$128.20	$128.20
Purchase #6	$209.53	10.527%	$231.5872	$231.59	$231.60	$231.60
Purchase #7	$225.75	13.530%	$256.294	$256.29	$256.30	$256.30
7 purchase totals =	$865.51		$957.8354	$957.83	$957.85	$957.90