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	$124.66	9.291%	$136.2422	$136.24	$136.25	$136.20
Purchase #2	$130.94	8.697%	$142.3279	$142.33	$142.35	$142.30
Purchase #3	$44.95	12.382%	$50.5157	$50.52	$50.50	$50.50
Purchase #4	$39.65	3.667%	$41.104	$41.10	$41.10	$41.10
Purchase #5	$182.86	9.419%	$200.0836	$200.08	$200.10	$200.10
Purchase #6	$151.50	6.151%	$160.8188	$160.82	$160.80	$160.80
Purchase #7	$105.62	11.867%	$118.1539	$118.15	$118.15	$118.20
7 purchase totals =	$780.18		$849.2461	$849.24	$849.25	$849.20