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	$160.40	10.688%	$177.5436	$177.54	$177.55	$177.50
Purchase #2	$62.69	5.709%	$66.269	$66.27	$66.25	$66.30
Purchase #3	$39.31	7.490%	$42.2543	$42.25	$42.25	$42.30
Purchase #4	$156.78	12.574%	$176.4935	$176.49	$176.50	$176.50
Purchase #5	$29.78	13.613%	$33.834	$33.83	$33.85	$33.80
Purchase #6	$185.32	10.817%	$205.3661	$205.37	$205.35	$205.40
Purchase #7	$126.52	8.676%	$137.4969	$137.50	$137.50	$137.50
7 purchase totals =	$760.80		$839.2574	$839.25	$839.25	$839.30