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	$84.51	5.810%	$89.42	$89.42	$89.40	$89.40
Purchase #2	$135.97	6.223%	$144.4314	$144.43	$144.45	$144.40
Purchase #3	$143.55	12.771%	$161.8828	$161.88	$161.90	$161.90
Purchase #4	$50.82	3.465%	$52.5809	$52.58	$52.60	$52.60
Purchase #5	$195.46	7.741%	$210.5906	$210.59	$210.60	$210.60
Purchase #6	$10.60	12.278%	$11.9015	$11.90	$11.90	$11.90
Purchase #7	$132.67	13.800%	$150.9785	$150.98	$151.00	$151.00
7 purchase totals =	$753.58		$821.7857	$821.78	$821.85	$821.80