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	$46.70	11.215%	$51.9374	$51.94	$51.95	$51.90
Purchase #2	$233.84	8.383%	$253.4428	$253.44	$253.45	$253.40
Purchase #3	$90.30	8.329%	$97.8211	$97.82	$97.80	$97.80
Purchase #4	$176.93	13.260%	$200.3909	$200.39	$200.40	$200.40
Purchase #5	$126.52	10.158%	$139.3719	$139.37	$139.35	$139.40
Purchase #6	$79.64	3.851%	$82.7069	$82.71	$82.70	$82.70
Purchase #7	$78.64	9.732%	$86.2932	$86.29	$86.30	$86.30
7 purchase totals =	$832.57		$911.9642	$911.96	$911.95	$911.90