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	$6.82	9.326%	$7.456	$7.46	$7.45	$7.50
Purchase #2	$180.60	6.637%	$192.5864	$192.59	$192.60	$192.60
Purchase #3	$83.64	6.552%	$89.1201	$89.12	$89.10	$89.10
Purchase #4	$167.43	6.677%	$178.6093	$178.61	$178.60	$178.60
Purchase #5	$19.79	6.419%	$21.0603	$21.06	$21.05	$21.10
Purchase #6	$104.45	8.714%	$113.5518	$113.55	$113.55	$113.60
Purchase #7	$13.75	10.561%	$15.2021	$15.20	$15.20	$15.20
7 purchase totals =	$576.48		$617.5860	$617.59	$617.55	$617.70