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	$100.51	11.267%	$111.8345	$111.83	$111.85	$111.80
Purchase #2	$54.38	6.523%	$57.9272	$57.93	$57.95	$57.90
Purchase #3	$230.70	3.528%	$238.8391	$238.84	$238.85	$238.80
Purchase #4	$128.44	7.671%	$138.2926	$138.29	$138.30	$138.30
Purchase #5	$115.57	9.625%	$126.6936	$126.69	$126.70	$126.70
Purchase #6	$179.90	10.559%	$198.8956	$198.90	$198.90	$198.90
Purchase #7	$61.88	8.374%	$67.0618	$67.06	$67.05	$67.10
7 purchase totals =	$871.38		$939.5444	$939.54	$939.60	$939.50