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	$131.86	12.320%	$148.1052	$148.11	$148.10	$148.10
Purchase #2	$221.55	10.463%	$244.7308	$244.73	$244.75	$244.70
Purchase #3	$198.93	5.861%	$210.5893	$210.59	$210.60	$210.60
Purchase #4	$94.51	12.485%	$106.3096	$106.31	$106.30	$106.30
Purchase #5	$139.85	13.630%	$158.9116	$158.91	$158.90	$158.90
Purchase #6	$24.48	11.725%	$27.3503	$27.35	$27.35	$27.40
Purchase #7	$138.28	3.835%	$143.583	$143.58	$143.60	$143.60
7 purchase totals =	$949.46		$1,039.5798	$1,039.58	$1,039.60	$1,039.60