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	$225.34	13.678%	$256.162	$256.16	$256.15	$256.20
Purchase #2	$192.29	10.220%	$211.942	$211.94	$211.95	$211.90
Purchase #3	$214.72	5.826%	$227.2296	$227.23	$227.25	$227.20
Purchase #4	$38.86	3.160%	$40.088	$40.09	$40.10	$40.10
Purchase #5	$187.33	7.209%	$200.8346	$200.83	$200.85	$200.80
Purchase #6	$154.91	8.678%	$168.3531	$168.35	$168.35	$168.40
Purchase #7	$216.55	8.102%	$234.0949	$234.09	$234.10	$234.10
7 purchase totals =	$1,230.00		$1,338.7042	$1,338.69	$1,338.75	$1,338.70