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	$16.35	3.567%	$16.9332	$16.93	$16.95	$16.90
Purchase #2	$213.87	5.721%	$226.1055	$226.11	$226.10	$226.10
Purchase #3	$53.89	10.719%	$59.6665	$59.67	$59.65	$59.70
Purchase #4	$37.76	12.692%	$42.5525	$42.55	$42.55	$42.60
Purchase #5	$155.92	10.509%	$172.3056	$172.31	$172.30	$172.30
Purchase #6	$211.88	8.508%	$229.9068	$229.91	$229.90	$229.90
Purchase #7	$134.93	5.579%	$142.4577	$142.46	$142.45	$142.50
7 purchase totals =	$824.60		$889.9278	$889.94	$889.90	$890.00