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	$146.87	5.262%	$154.5983	$154.60	$154.60	$154.60
Purchase #2	$130.78	9.452%	$143.1413	$143.14	$143.15	$143.10
Purchase #3	$8.59	11.873%	$9.6099	$9.61	$9.60	$9.60
Purchase #4	$102.70	10.624%	$113.6108	$113.61	$113.60	$113.60
Purchase #5	$31.52	7.596%	$33.9143	$33.91	$33.90	$33.90
Purchase #6	$103.53	7.266%	$111.0525	$111.05	$111.05	$111.10
Purchase #7	$36.93	3.177%	$38.1033	$38.10	$38.10	$38.10
7 purchase totals =	$560.92		$604.0304	$604.02	$604.00	$604.00