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	$37.58	5.366%	$39.5965	$39.60	$39.60	$39.60
Purchase #2	$50.37	4.205%	$52.4881	$52.49	$52.50	$52.50
Purchase #3	$53.88	7.373%	$57.8526	$57.85	$57.85	$57.90
Purchase #4	$198.69	12.471%	$223.4686	$223.47	$223.45	$223.50
Purchase #5	$131.40	8.336%	$142.3535	$142.35	$142.35	$142.40
Purchase #6	$97.51	10.324%	$107.5769	$107.58	$107.60	$107.60
Purchase #7	$111.30	6.493%	$118.5267	$118.53	$118.55	$118.50
7 purchase totals =	$680.73		$741.8629	$741.87	$741.90	$742.00