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	$36.63	6.153%	$38.8838	$38.88	$38.90	$38.90
Purchase #2	$43.44	10.314%	$47.9204	$47.92	$47.90	$47.90
Purchase #3	$187.98	6.128%	$199.4994	$199.50	$199.50	$199.50
Purchase #4	$110.74	10.440%	$122.3013	$122.30	$122.30	$122.30
Purchase #5	$111.55	5.416%	$117.5915	$117.59	$117.60	$117.60
Purchase #6	$163.72	9.269%	$178.8952	$178.90	$178.90	$178.90
Purchase #7	$105.64	5.289%	$111.2273	$111.23	$111.25	$111.20
7 purchase totals =	$759.70		$816.3189	$816.32	$816.35	$816.30