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	$233.69	12.815%	$263.6374	$263.64	$263.65	$263.60
Purchase #2	$143.47	4.762%	$150.302	$150.30	$150.30	$150.30
Purchase #3	$20.30	7.868%	$21.8972	$21.90	$21.90	$21.90
Purchase #4	$19.50	4.456%	$20.3689	$20.37	$20.35	$20.40
Purchase #5	$148.49	6.756%	$158.522	$158.52	$158.50	$158.50
Purchase #6	$75.93	9.766%	$83.3453	$83.35	$83.35	$83.30
Purchase #7	$137.88	3.397%	$142.5638	$142.56	$142.55	$142.60
7 purchase totals =	$779.26		$840.6366	$840.64	$840.60	$840.60