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	$36.49	12.422%	$41.0228	$41.02	$41.00	$41.00
Purchase #2	$82.90	7.775%	$89.3455	$89.35	$89.35	$89.30
Purchase #3	$223.78	9.688%	$245.4598	$245.46	$245.45	$245.50
Purchase #4	$176.89	8.641%	$192.1751	$192.18	$192.20	$192.20
Purchase #5	$80.65	3.522%	$83.4905	$83.49	$83.50	$83.50
Purchase #6	$86.68	3.643%	$89.8378	$89.84	$89.85	$89.80
Purchase #7	$107.49	6.180%	$114.1329	$114.13	$114.15	$114.10
7 purchase totals =	$794.88		$855.4644	$855.47	$855.50	$855.40