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	$139.70	11.283%	$155.4624	$155.46	$155.45	$155.50
Purchase #2	$38.45	3.777%	$39.9023	$39.90	$39.90	$39.90
Purchase #3	$157.57	6.546%	$167.8845	$167.88	$167.90	$167.90
Purchase #4	$7.50	5.290%	$7.8968	$7.90	$7.90	$7.90
Purchase #5	$133.42	9.541%	$146.1496	$146.15	$146.15	$146.10
Purchase #6	$210.46	7.603%	$226.4613	$226.46	$226.45	$226.50
Purchase #7	$238.89	7.790%	$257.4995	$257.50	$257.50	$257.50
7 purchase totals =	$925.99		$1,001.2564	$1,001.25	$1,001.25	$1,001.30